cel comes on at 40 mph

[uawpipefitter]

cel came on a couple of days ago, put the scanner on it & got codes 33,41,53changed the tps,&egr valve scanned it again got code 34.put a new egr sensor on than got code 41,23. didnt have time to investigate before work and on the way to work the cel came on at 40 mph and went off when i would come to a stop. this would repeat during my drive to work. i have a 94 sport with a 4.0 and a 5 speed. the 33 & 34 codes deal with the egr ,the 41 is for o2 sensor which i plan on changing. the 23 is tps signal voltage out of self-test specs. these codes were KOEO. i have been reading threads and you guys are saying that 94s are 3 digit codes not true. the only 3 digit code i got was when i did the KOER test and it was 326 which is egr sensor signal voltage lower than expected.the thing runs fine just need some ideas on why the cel comes.

[MrShorty]

SOP when resolving EEC-IV codes is to resolve KOEO codes first. 1st step would be to identify which of those codes are KOEO codes and which are CM. Recognize that KOEo codes almost have to be electrical in nature, so the next step would be to get a wiring diagram showing the effected sensor's circuit.

[uawpipefitter]

mr shorty so you are saying that more than likely its a wiring problem? i did test the voltage on the plug to the tps & it was lower than the manual said it should be. it was 3.76 and the book said 5.0 plus or minus 0.1. if its a short it would be easier just to take it somewhere & have it looked at.

[MrShorty]

mr shorty so you are saying that more than likely its a wiring problem?

That isn't exactly what I was trying to say, but it is a valid point. DTC's point to out of range conditions in a circuit or a system. By itself, a DTC can rarely if ever tell you what component is bad.

The point I wanted to make is that, anytime you have a list of codes, the first thing to do is to determine which codes are KOEO codes (sometimes referred to as KOEO hard fault codes) and which are CM (continuous memory or KOEO soft fault codes). Your diagnosis will then focus on the KOEO code(s).

If you don't know how to distinguish them, review your instructions and my "notes on pulling EEc-IV codes".

if its a short it would be easier just to take it somewhere & have it looked at.

Sometimes this is true -- it depends on your skill level with electrical diagnosis. For the most part, these circuits aren't real complicated for someone who has a good feel for DC electricity. If you're not comfortable with it, there's nothing wrong with paying someone to do it for you.

One last note: those voltage readings at the TPS don't mean much unless we know which two leads you're testing.