Most Common Sensor Faults WITHOUT a Check Engine Light

[Kiqman]

The ECM is supposed to throw a code just about anytime a sensor malfunctions. We all know that just because a check engine light does not come on does not mean that all sensors are operational. I thought I'd start a poll to find the most common sensor faults owners have experienced that never threw a check engine light. If you choose "other" please post what sensor malfunctioned.

 

[NEK5]

well the SE light might of been on...but mine no workie

 

[Kiqman]

Sometimes I think I'd be happier if I just disconnected mine! When it comes on it means my Saturday is shot.

 

[Thunder]

By far the most common failure without a CEL is the dist module.
When it fails it throws a 12. which is also the code that shows the ECM is functioning and in diagnostic mode. Code 12 =ignition on. No spark detected.
so if you have a stumble, miss, or engine dies and all you get is a 12. the first thing to suspect is the dist(ignition control ) module.

All the other sensors you listed wil throw a code(s) if they fail. The trick is in knowing how to understand what the ECM is telling you.

 

[Kiqman]

In a perfect world

All the other sensors you listed wil throw a code(s) if they fail. The trick is in knowing how to understand what the ECM is telling you.

Theory will tell you this statement is true - has to be true. Shop experience tells a different story some would say. Variable resistance sensors can give readings that are within expected parameters but still bad readings. The lack of a check engine light, in my opinion, does not mean that all the sensors are functioning and reporting as designed.

 

[Thunder]

The lack of a check engine light, in my opinion, does not mean that all the sensors are functioning and reporting as designed.

True. But I never said in my post or mentioned a CEL. I talked about trouble codes. A sensor can mal function and not throw a code OR CEL that indicates the sensor involved. But. If one sensor/control fails. But no code is set for it. It usually effects the engine somewhere else and it will set a code on another sensor. EX: A malfunctioning MAF at a certain rpm usually wont set a code BUT The O2 sensor may read a lean condition and set a o2 lean code.
Most people would read that and replace the O2 and still ave the problem.. But. You have to think....... Hmmm...................Why is it lean? .............Hmm could be a Vaccum leak or a bad maf. Do your DD and fix it
Codes or even the lack of one tell a lot about how the engine is running.
Thats why I said "The trick is in knowing how to understand what the ECM is telling you.'

 

[opfor2]

By far the most common failure without a CEL is the dist module.

I'll second the ignition module, what a Paine in da A$$ this is to diagnose.

 

[4xcrazy]

had a friend replace the computer box (brain),,,no CEL and corrected whatever problem there was....We even changed out the fuel pump thinking low fuel pressure, O2 sensor, couple of smaller sensors as well.