94 xlt koeo code 175

[bigku1]

I have searched forum for info on code 175 with no luck. I'm new at this and would appreciate any info on how to troubleshoot this code. I get this code consistenly when CEL comes on. Engine rough at start then smooth's out.

 

[bigku1]

Here is the code def:

175
(M)
Oxygen sensor not switching - system was at adaptive limits - Left or Front HO2S - Fuel control

I need a translation.....

 

[MrShorty]

175 should be a CM code, not a KOEO code (read/review my notes on pulling EEC-IV codes to review the difference between KOEO and CM codes).

Can I assume it passed KOEO? Did you run the KOER test?

To understand the basic translation, you might review the "primer on electronic engine controls" thread. I believe that thread has a basic description of how the PCM controls fuel mixture, and how the O2 sensor is the "point man" of a feedback loop that helps control fuel mixture. Basically what this code means, is that the feedback loop is demanding more/less fuel than the PCM's programming will allow. O2 sensor codes are sometimes among the most difficult to diagnose, and this one can be particularly troublesome because, without another code or other information, we don't even know if the computer is seeing a lean or rich condition. Left/Front refers to the driver's side O2 sensor.

Among the steps I might take:

Run KOER test, if you haven't already.
Check fuel pressure.
Pull a spark plug to see if the plug's condition indicates a rich or lean condition.
Does exhaust stream indicate rich or lean?
Put a voltmeter on the O2 sensor signal circuit to see what it is seeing (if you have access to a good scanner, you should be able to look at this with the scanner).

 

[bigku1]

Yes this a CM code. I will try the engine running test.
I did the engine running test and the only code I received was
code 536.
I will also add, the CEL comes on after a few minutes of driving,
then usually goes off after a few minutes, normally when I
am on flat surface, then on incline it will come back
on. This the normal pattern for the CEL.

 

[MrShorty]

KOER 536 is often operator error. Did you press the brake after engine id was output (review my notes on pulling EEc-IV codes thread if you need help with the test protocol)?

This suggests that the fault is intermittent, which is likely going to make it that much more difficult to track down.

I will also add, the CEL comes on after a few minutes of driving,

Will it also come on after a few minutes sitting at idle, or only after driving?

I might still put a fuel pressure gauge on it, especially if you can rig it up so you can see if the fuel pressure is doing something funny in those first few minutes of driving.

A scanner or voltmeter monitoring the O2 sensor signal during those few minutes of driving could still be useful.

This one could be a real challenge to troubleshoot. If it had been a long time since changing that sensor, I might just change the sensor (in the name of maintenance) and see if that fixed it, but, maybe not, too.

 

[bigku1]

Changed O2 sensor, no longer getting code 175. Let the fun begin, now getting 185 and 186. Am going to clean MAF sensor and will post outcome..

 

[MrShorty]

It looks like something still isn't right in fuel control. Let us know what happens after cleaning the MAF.

 

[bigku1]

Cleaned MAF sensor and have not had a CEL for 3 days.

Just my my 2 cents: The first thing I would do if I got any kind of fuel control code, I would take 15 minutes and spend no money and clean the MAF sensor before I did anything else.

Thanks Mr. Shorty for all your input, I really appreciate it.

If other codes show up I will post.