Heated seat fault testing and diagnosis
01-18-2014, 12:32 AM
#1
Heated seat fault testing and diagnosis
Heated seat not working? This seems to be a common fault, most often with the lower seat heating element rather then the back element. The typical failure is quite easy to diagnose. This only applies to those who only have heated seats. Those who have heated and cooled seats have a different system using a component referred to as TED. Those aren't quite as simple.
In the typical heat only system, the signal starts at the FCIM when you push the switch. From there the signal uses the CAN network and goes thru the HVAC module and then on to the heated seat module.
This test is done after the heated seat module, right at the connector to the lower element. The first part of the test involves checking for voltage at the connector, and if there is voltage then you know that all three of the modules involved are working as intended and that no network faults are to blame for your lack of heat at the seats.
The seat uses two elements, one for the lower, and one for the back. They are wired in series and so they share the available voltage and current. Like old school Christmas lights if one is burnt out, then neither one will work. Also, because they are wired in series, the voltage in and out is split. So if available voltage is 14 volts, and the resistance of both elements is the same, then the voltage into the first element is 14v, out of the first element and into the second 7v, and finally out of the second element will be 0v as it heads off towards ground.
Now, to what most really care about. Underneath the front of the seat, clipped to a crossbrace, you will see a connector with four wires. This is the connector for the lower element. Of those four wires, the two grey wires go to a sensor, and the red and black wires go to the lower element. You will be checking for voltage on these last two wires.
So, the red wire is the power feed to the lower element. Leave the connector hooked up for both of these tests.
If you push the switch, and it lights up, and you back probe the red wire at the connector and it has 13-14 volts then you know that the modules and network are operating and sending the signal and voltage all the way to the heating elements. If you have no voltage at the red wire then you should probably take the truck to someone with a scan tool and some diagnostic equipment as it is probably not such a simple fix.
After confirming voltage on the red wire then the next test will be to check for voltage on the black wire. If the lower pad is intact then there will be voltage on the black wire. If there is no voltage on the black wire then the lower element is burnt out (this is where most will find the fault). If you pull the cover back you will likely see charred foam where the element is burnt open.
If there is voltage on the black wire, then that voltage will depend on the integrity of the back element and the ground connection after that. If the system is operating correctly then you should see 6-7v on that black wire as it splits the voltage with the back element. If the voltage is 13-14v then there is an open circuit after the lower element. Either the back element is bad, or the ground is bad.
If (however unlikely) you have 13-14v on the black wire indicating a bad back element or ground then you will need to unzip the seat back. There you will find the two wire connector to the back element. If you have 13-14v in and out of that connector then the ground is bad. If you have 13-14v in and nothing out then the rear element is bad.
There really isn't much to this with the typical open element no code fault. This works for both driver side and passenger side.
Oddly enough, I had this very fault (among other things where the dealer had my truck for 3 weeks). They ended up replacing the 5.0 for internal damage and forgot to finish the seat heater fault. But they did leave the back of the seat completely unzipped. I scheduled it to go back in a couple days later to finish the job.
Given the lack of quality work I decided to diagnose it myself before it went in. I diagnosed the bad lower element and shared it with my service writer. He said that the tech had diagnosed it as a bad hvac module. I told him that the tech could replace the module if he really wanted too, but he would still need the element as that was what was actually bad. Even after asking the service writer to make sure that he had an element in stock so it could be repaired quickly, he did not, and it took 3 days to repair my heated seat because they had to order the part. (They had no trouble ordering the hvac module ahead of time though).
On the RO when I got my truck back it states that the tech found BOTH front seats inop (when I had no issue with the passenger seat as we had been using it repetively). The RO states that he replaced the hvac module to correct the fault of neither seat working, then found that the driver seat was still inop. Then, he replaced the driver seat element. Way to shotgun a module at it and when it doesn't stick and fix the problem then find and fix the actual problem and then creatively write the RO to cover up your mistake! I'm surprised he didn't try to replace the FCIM and the heated seat module as well. Anyway, there is a whole long story there with the seat and the engine and other aspects that is probably best left for another time.
Hopefully this helps with some who may want to figure out why their seat heater does not work.
In the typical heat only system, the signal starts at the FCIM when you push the switch. From there the signal uses the CAN network and goes thru the HVAC module and then on to the heated seat module.
This test is done after the heated seat module, right at the connector to the lower element. The first part of the test involves checking for voltage at the connector, and if there is voltage then you know that all three of the modules involved are working as intended and that no network faults are to blame for your lack of heat at the seats.
The seat uses two elements, one for the lower, and one for the back. They are wired in series and so they share the available voltage and current. Like old school Christmas lights if one is burnt out, then neither one will work. Also, because they are wired in series, the voltage in and out is split. So if available voltage is 14 volts, and the resistance of both elements is the same, then the voltage into the first element is 14v, out of the first element and into the second 7v, and finally out of the second element will be 0v as it heads off towards ground.
Now, to what most really care about. Underneath the front of the seat, clipped to a crossbrace, you will see a connector with four wires. This is the connector for the lower element. Of those four wires, the two grey wires go to a sensor, and the red and black wires go to the lower element. You will be checking for voltage on these last two wires.
So, the red wire is the power feed to the lower element. Leave the connector hooked up for both of these tests.
If you push the switch, and it lights up, and you back probe the red wire at the connector and it has 13-14 volts then you know that the modules and network are operating and sending the signal and voltage all the way to the heating elements. If you have no voltage at the red wire then you should probably take the truck to someone with a scan tool and some diagnostic equipment as it is probably not such a simple fix.
After confirming voltage on the red wire then the next test will be to check for voltage on the black wire. If the lower pad is intact then there will be voltage on the black wire. If there is no voltage on the black wire then the lower element is burnt out (this is where most will find the fault). If you pull the cover back you will likely see charred foam where the element is burnt open.
If there is voltage on the black wire, then that voltage will depend on the integrity of the back element and the ground connection after that. If the system is operating correctly then you should see 6-7v on that black wire as it splits the voltage with the back element. If the voltage is 13-14v then there is an open circuit after the lower element. Either the back element is bad, or the ground is bad.
If (however unlikely) you have 13-14v on the black wire indicating a bad back element or ground then you will need to unzip the seat back. There you will find the two wire connector to the back element. If you have 13-14v in and out of that connector then the ground is bad. If you have 13-14v in and nothing out then the rear element is bad.
There really isn't much to this with the typical open element no code fault. This works for both driver side and passenger side.
Oddly enough, I had this very fault (among other things where the dealer had my truck for 3 weeks). They ended up replacing the 5.0 for internal damage and forgot to finish the seat heater fault. But they did leave the back of the seat completely unzipped. I scheduled it to go back in a couple days later to finish the job.
Given the lack of quality work I decided to diagnose it myself before it went in. I diagnosed the bad lower element and shared it with my service writer. He said that the tech had diagnosed it as a bad hvac module. I told him that the tech could replace the module if he really wanted too, but he would still need the element as that was what was actually bad. Even after asking the service writer to make sure that he had an element in stock so it could be repaired quickly, he did not, and it took 3 days to repair my heated seat because they had to order the part. (They had no trouble ordering the hvac module ahead of time though).
On the RO when I got my truck back it states that the tech found BOTH front seats inop (when I had no issue with the passenger seat as we had been using it repetively). The RO states that he replaced the hvac module to correct the fault of neither seat working, then found that the driver seat was still inop. Then, he replaced the driver seat element. Way to shotgun a module at it and when it doesn't stick and fix the problem then find and fix the actual problem and then creatively write the RO to cover up your mistake! I'm surprised he didn't try to replace the FCIM and the heated seat module as well. Anyway, there is a whole long story there with the seat and the engine and other aspects that is probably best left for another time.
Hopefully this helps with some who may want to figure out why their seat heater does not work.
The following 4 users liked this post by 6874:
The following 3 users liked this post by 6874:
01-18-2014, 09:27 PM
#3
Well my driver seat is without heat right now. I knew about the two elements wired in series, but had no idea about how I could check for a fault. Sounds like way too much work for me, guess I'll have to survive a few more cool months.
04-19-2014, 10:17 AM
#4
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Heated seat not working? This seems to be a common fault, most often with the lower seat heating element rather then the back element. The typical failure is quite easy to diagnose. This only applies to those who only have heated seats. Those who have heated and cooled seats have a different system using a component referred to as TED. Those aren't quite as simple.
In the typical heat only system, the signal starts at the FCIM when you push the switch. From there the signal uses the CAN network and goes thru the HVAC module and then on to the heated seat module.
This test is done after the heated seat module, right at the connector to the lower element. The first part of the test involves checking for voltage at the connector, and if there is voltage then you know that all three of the modules involved are working as intended and that no network faults are to blame for your lack of heat at the seats.
The seat uses two elements, one for the lower, and one for the back. They are wired in series and so they share the available voltage and current. Like old school Christmas lights if one is burnt out, then neither one will work. Also, because they are wired in series, the voltage in and out is split. So if available voltage is 14 volts, and the resistance of both elements is the same, then the voltage into the first element is 14v, out of the first element and into the second 7v, and finally out of the second element will be 0v as it heads off towards ground.
Now, to what most really care about. Underneath the front of the seat, clipped to a crossbrace, you will see a connector with four wires. This is the connector for the lower element. Of those four wires, the two grey wires go to a sensor, and the red and black wires go to the lower element. You will be checking for voltage on these last two wires.
So, the red wire is the power feed to the lower element. Leave the connector hooked up for both of these tests.
If you push the switch, and it lights up, and you back probe the red wire at the connector and it has 13-14 volts then you know that the modules and network are operating and sending the signal and voltage all the way to the heating elements. If you have no voltage at the red wire then you should probably take the truck to someone with a scan tool and some diagnostic equipment as it is probably not such a simple fix.
After confirming voltage on the red wire then the next test will be to check for voltage on the black wire. If the lower pad is intact then there will be voltage on the black wire. If there is no voltage on the black wire then the lower element is burnt out (this is where most will find the fault). If you pull the cover back you will likely see charred foam where the element is burnt open.
If there is voltage on the black wire, then that voltage will depend on the integrity of the back element and the ground connection after that. If the system is operating correctly then you should see 6-7v on that black wire as it splits the voltage with the back element. If the voltage is 13-14v then there is an open circuit after the lower element. Either the back element is bad, or the ground is bad.
If (however unlikely) you have 13-14v on the black wire indicating a bad back element or ground then you will need to unzip the seat back. There you will find the two wire connector to the back element. If you have 13-14v in and out of that connector then the ground is bad. If you have 13-14v in and nothing out then the rear element is bad.
There really isn't much to this with the typical open element no code fault. This works for both driver side and passenger side.
Oddly enough, I had this very fault (among other things where the dealer had my truck for 3 weeks). They ended up replacing the 5.0 for internal damage and forgot to finish the seat heater fault. But they did leave the back of the seat completely unzipped. I scheduled it to go back in a couple days later to finish the job.
Given the lack of quality work I decided to diagnose it myself before it went in. I diagnosed the bad lower element and shared it with my service writer. He said that the tech had diagnosed it as a bad hvac module. I told him that the tech could replace the module if he really wanted too, but he would still need the element as that was what was actually bad. Even after asking the service writer to make sure that he had an element in stock so it could be repaired quickly, he did not, and it took 3 days to repair my heated seat because they had to order the part. (They had no trouble ordering the hvac module ahead of time though).
On the RO when I got my truck back it states that the tech found BOTH front seats inop (when I had no issue with the passenger seat as we had been using it repetively). The RO states that he replaced the hvac module to correct the fault of neither seat working, then found that the driver seat was still inop. Then, he replaced the driver seat element. Way to shotgun a module at it and when it doesn't stick and fix the problem then find and fix the actual problem and then creatively write the RO to cover up your mistake! I'm surprised he didn't try to replace the FCIM and the heated seat module as well. Anyway, there is a whole long story there with the seat and the engine and other aspects that is probably best left for another time.
Hopefully this helps with some who may want to figure out why their seat heater does not work.
In the typical heat only system, the signal starts at the FCIM when you push the switch. From there the signal uses the CAN network and goes thru the HVAC module and then on to the heated seat module.
This test is done after the heated seat module, right at the connector to the lower element. The first part of the test involves checking for voltage at the connector, and if there is voltage then you know that all three of the modules involved are working as intended and that no network faults are to blame for your lack of heat at the seats.
The seat uses two elements, one for the lower, and one for the back. They are wired in series and so they share the available voltage and current. Like old school Christmas lights if one is burnt out, then neither one will work. Also, because they are wired in series, the voltage in and out is split. So if available voltage is 14 volts, and the resistance of both elements is the same, then the voltage into the first element is 14v, out of the first element and into the second 7v, and finally out of the second element will be 0v as it heads off towards ground.
Now, to what most really care about. Underneath the front of the seat, clipped to a crossbrace, you will see a connector with four wires. This is the connector for the lower element. Of those four wires, the two grey wires go to a sensor, and the red and black wires go to the lower element. You will be checking for voltage on these last two wires.
So, the red wire is the power feed to the lower element. Leave the connector hooked up for both of these tests.
If you push the switch, and it lights up, and you back probe the red wire at the connector and it has 13-14 volts then you know that the modules and network are operating and sending the signal and voltage all the way to the heating elements. If you have no voltage at the red wire then you should probably take the truck to someone with a scan tool and some diagnostic equipment as it is probably not such a simple fix.
After confirming voltage on the red wire then the next test will be to check for voltage on the black wire. If the lower pad is intact then there will be voltage on the black wire. If there is no voltage on the black wire then the lower element is burnt out (this is where most will find the fault). If you pull the cover back you will likely see charred foam where the element is burnt open.
If there is voltage on the black wire, then that voltage will depend on the integrity of the back element and the ground connection after that. If the system is operating correctly then you should see 6-7v on that black wire as it splits the voltage with the back element. If the voltage is 13-14v then there is an open circuit after the lower element. Either the back element is bad, or the ground is bad.
If (however unlikely) you have 13-14v on the black wire indicating a bad back element or ground then you will need to unzip the seat back. There you will find the two wire connector to the back element. If you have 13-14v in and out of that connector then the ground is bad. If you have 13-14v in and nothing out then the rear element is bad.
There really isn't much to this with the typical open element no code fault. This works for both driver side and passenger side.
Oddly enough, I had this very fault (among other things where the dealer had my truck for 3 weeks). They ended up replacing the 5.0 for internal damage and forgot to finish the seat heater fault. But they did leave the back of the seat completely unzipped. I scheduled it to go back in a couple days later to finish the job.
Given the lack of quality work I decided to diagnose it myself before it went in. I diagnosed the bad lower element and shared it with my service writer. He said that the tech had diagnosed it as a bad hvac module. I told him that the tech could replace the module if he really wanted too, but he would still need the element as that was what was actually bad. Even after asking the service writer to make sure that he had an element in stock so it could be repaired quickly, he did not, and it took 3 days to repair my heated seat because they had to order the part. (They had no trouble ordering the hvac module ahead of time though).
On the RO when I got my truck back it states that the tech found BOTH front seats inop (when I had no issue with the passenger seat as we had been using it repetively). The RO states that he replaced the hvac module to correct the fault of neither seat working, then found that the driver seat was still inop. Then, he replaced the driver seat element. Way to shotgun a module at it and when it doesn't stick and fix the problem then find and fix the actual problem and then creatively write the RO to cover up your mistake! I'm surprised he didn't try to replace the FCIM and the heated seat module as well. Anyway, there is a whole long story there with the seat and the engine and other aspects that is probably best left for another time.
Hopefully this helps with some who may want to figure out why their seat heater does not work.
05-29-2016, 07:06 PM
#5
Senior Member
OK...help me interpret these weird results:
Drivers side
Red--12V
Black--12V
Passenger side
Red--12V
Black--0V
I'm pretty sure I only have the seat, not the back heated on my passenger side, at least that's how it's always worked.
Here's the strange part. these voltages are present, regardless of the switch setting.
Whether the switch is set to high, low or off, these numbers don't change.
The switch stays illuminated, as it always has.
I thought I had the wrong connector, but it fits the description above perfectly. It's a 4-pin connector. Red and black are at diagonally opposite corners. The other two wires are gray.
Any ideas before I start ripping seats apart?
Drivers side
Red--12V
Black--12V
Passenger side
Red--12V
Black--0V
I'm pretty sure I only have the seat, not the back heated on my passenger side, at least that's how it's always worked.
Here's the strange part. these voltages are present, regardless of the switch setting.
Whether the switch is set to high, low or off, these numbers don't change.
The switch stays illuminated, as it always has.
I thought I had the wrong connector, but it fits the description above perfectly. It's a 4-pin connector. Red and black are at diagonally opposite corners. The other two wires are gray.
Any ideas before I start ripping seats apart?
11-09-2016, 12:54 PM
#6
I know it's an old thread, but I found this and was a huge help. Simplified it so I could test and find that my drivers lower was the issue. Replaced it and found it burned pretty bad, works great now. Thanks for the write up.
12-13-2018, 01:41 PM
#7
Bumping this thread up because it sounds exactly like what is happening to my driver's side seat. It gets hot enough on high to start burning my thighs, and then doesn't hardly heat up at all when on the low setting. I'll break out the DMM after I get back from my trip this weekend and check out and see what is going on with it.
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12-18-2018, 08:35 AM
#8
i have a 2012 f150 lariat and both seats don't work. I got the truck from my dad before he passed. it has 24000 miles and im sure the heat was never used. my truck does not have the hvac module, it only has a dcsm module. (part # BU5Z-14C724-A). I took the module apart and test it. I have 14 volts on the driver and passenger heat request. I have 4 volts on driver low heat status and 0 volts on high heat status. on the passenger seat I have 5 volts on the low heat status and 0 volts on the high heat status. these reading are the same with the truck running and switches on or off. all fuses are good and since both seats don't work would it be the module or something else. thanks
12-18-2018, 08:54 AM
#9
Senior Member
i have a 2012 f150 lariat and both seats don't work. I got the truck from my dad before he passed. it has 24000 miles and im sure the heat was never used. my truck does not have the hvac module, it only has a dcsm module. (part # BU5Z-14C724-A). I took the module apart and test it. I have 14 volts on the driver and passenger heat request. I have 4 volts on driver low heat status and 0 volts on high heat status. on the passenger seat I have 5 volts on the low heat status and 0 volts on the high heat status. these reading are the same with the truck running and switches on or off. all fuses are good and since both seats don't work would it be the module or something else. thanks
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Dan W (12-18-2018)
11-04-2019, 04:03 PM
#10
I tested the plug at pos/neg with the switch and lights on and got zero for both sides, even though my passenger side works. Did I do it wrong?
EDIT: The *** element was burned out when i opened the seat to look. Replaced it and now everything runs great.
EDIT: The *** element was burned out when i opened the seat to look. Replaced it and now everything runs great.
Last edited by Pitbull2o08; 03-29-2020 at 08:19 AM.