Hey everyone. For the record my truck SEEMS to be running fine, purrs like a kitten. But I bought this code reader because I was wanting to see if anything was wrong with my truck and my dad's 93 4.9 because my check engine light doesn't work in my 1991 4.9. I ended up getting 3 codes. I need insight on what exactly these are and how to fix them. I'll also put what the manual says the codes are. The truck these codes came from are my 1991 4.9. Auto transmission if that matters with 226k on the truck.

Code 181: HEGO (HO2S) sensor fault unable to switch/lean during part throttle


Code 332: Insufficient EGR flow detected


Code 634: Manual Lever Position sensor voltage higher or lower than expected or A/C on

By the way all these tests were done with KOEO because the manual said not to do the KOER test until you get a code 11 with the KOEO test.

 

The order the codes are listed is the order they come up on the code reader? Repair codes in the same order they appear.

With that said sounds like a slow responding O2 sensor. Replace the sensor with new or if on a budget try pulling it out and burning any excess carbon off the O2 with a torch. Remove battery cable for 15 minutes, replace sensor and drive for a day or so then retest. Fix the next code in sequence, sometimes might only have to fix one or two and the other codes will go away.

 

No the order they come in was 634, 181, and 332 if I'm not mistaken. Is there only 1 o2 sensor before the cat?

 

Yes. That 634 is a strange one, shouldn't affect performance and doubt it would turn cel on if it worked.

 

Just to let everyone know.. I guess I'm a true man and didn't follow directions lol. I tested my vehicle while it was cold before I posted this. I drove it to work and while it was hot I tested it again and got code 111 which is system pass. Lol so follow directions in manuals! They're there for a reason lol.

 

I know you found what was wrong with your readings
but anyways
here is the info on the 634 code:
The temprature selector (manual lever) on the a/c control panel has a sensor on it to tell the computer that you want a/c or heater or defroster so it knows to turn the compressor on. The sensor is shorted and is sending high voltage to the computer and causing a code

 

Hmm I don't have that 634 code now though. I'll do the KOER test tomorrow

 

So today I ran a KOER test. I am now sad.

My results are code 332 again, and a new one. The new one is code 225. 225 is knock sensor fault during dynamic response test. And yes during the 3 tests I took just to make sure, the engine was warm and I did floor the gas pedal at the specific given time. I have no idea what a knock sensor is and what it's for so can someone help me?

 

The knock sensor (if used) is there to detect spark knock which is also called pinging or preignition. This is where the fuel ignites prematurely in multiple places within the cylinder, and creates shock waves that you can hear. Sounds like glass marbles inside the engine. The knock sensor listens for this and will retard ignition timing to try and stop it.

 

Ok I just talked to a mechanic and he said that he wasn't sure if 1991 4.9s had knock sensors... Is this true? And what symptoms of a bad knock sensor would I have?