P1285- CHT sensor
08-14-2015, 12:26 PM
#1
P1285- CHT sensor
2004 f150 5.4 V8 giving false overheating. I'm almost positive it's the CHT sensor but I need help finding it. I've been told it's near the thermostat, on the back side of the motor, under the intake manifold, behind the alternator, etc. I'd really like some closure on this so I can get this fixed asap. Thanks!
08-15-2015, 12:27 AM
#2
LightningRod
@dmummy
I realize P1285 indicates CHT overtemp condition based on the "reading the ECU is getting from the CHT sensor. However, there are a couple of other possitilities such as wiring / connection problems. I can tell you -from experience- that is extreem to casually attempt replacing it. It's located UNDER the Intake Manifold in the cylinder head between intake ports of cyl 2 & 3 and even removing the Alternator and Water crossover manifold there would not be enough clearance to reach it as the manifold "resonance chamber" fills the entire valley. The intake manifold has to be removed.
Also, numerous engine functions / perameters are dependent on it. You have no coolant temp sensor and Coolant Temp is calculated based upon CHT signal. You can't achieve Closed Loop until coolant temp (calculation) is sufficient, and you'll get a P0125 code - or P0217. The PCM will go into "limp mode". Also, by monitoring the OBDII signal from the CHT, you can see the ECU do a recalibration procedure on the CHT every run cycle.
Check / clean wiring connections to the ECU. Flush cooling system and replace coolant and even the thermostat (an easy cheap effort) and make sure to burp it (nose uphill and idle for a while to get air out) before going for the CHT.
This article might help diagnose it: http://www.searchautoparts.com/motor...ure-cht-sensor
I would recommend trying everything else in the book before tackling that. Checking out this link might help: https://www.f150forum.com/f4/temp-gaug-295494/
Good luck
I realize P1285 indicates CHT overtemp condition based on the "reading the ECU is getting from the CHT sensor. However, there are a couple of other possitilities such as wiring / connection problems. I can tell you -from experience- that is extreem to casually attempt replacing it. It's located UNDER the Intake Manifold in the cylinder head between intake ports of cyl 2 & 3 and even removing the Alternator and Water crossover manifold there would not be enough clearance to reach it as the manifold "resonance chamber" fills the entire valley. The intake manifold has to be removed.
Also, numerous engine functions / perameters are dependent on it. You have no coolant temp sensor and Coolant Temp is calculated based upon CHT signal. You can't achieve Closed Loop until coolant temp (calculation) is sufficient, and you'll get a P0125 code - or P0217. The PCM will go into "limp mode". Also, by monitoring the OBDII signal from the CHT, you can see the ECU do a recalibration procedure on the CHT every run cycle.
Check / clean wiring connections to the ECU. Flush cooling system and replace coolant and even the thermostat (an easy cheap effort) and make sure to burp it (nose uphill and idle for a while to get air out) before going for the CHT.
This article might help diagnose it: http://www.searchautoparts.com/motor...ure-cht-sensor
I would recommend trying everything else in the book before tackling that. Checking out this link might help: https://www.f150forum.com/f4/temp-gaug-295494/
Good luck