Pulled the following codes off my 95 Mystique 2.5L atx today (EEC-IV):
172 Heated Exhaust Gas Oxygen (HEGO) sensor - voltage signal indicates "lean" (Bank #1)
538 - Insufficient RPM change during dynamic response test (engine run self-test) or invalid cylinder balance test - throttle position movement or invalid cylinder balance test - cylinder identification problems.
Well, that narrows it down???
Any one had a throttle position sensor go bad? What are the symptoms?
The 538 happens if you don't goose it for the "goose test". You have to blip the throttle at a certain time if you do the KOER (Key on engine running) test. You had the engine running during the test, yes?
The 172 code means your oxygen sensor on the back of the engine (right by the firewall) needs replacing. Oh the joys of changing that one!
Replace the O2 sensor and you should be golden.
-Lance
Lance Kinley
CEG Webmaster
95 SE, "Cassandra"
10 years!
Thanks for the post. I changed the o2 sensor by the firewall. Still got a CEL. It was different, very short lived. Since I have 60,000 on it, I replaced the other one also. Reset computer, no more CEL, and runs like new.
Also spray the MAF wires with electronic parts cleaner. I blast mine clean every time I change the air filter. Vacuum leak(s) will do it too. Lance is the king of the intake seals.
I had already done that leading up to the replacement of the O2 sensor. Actually, I used carb cleaner, followed up with brake cleaner as outlined elsewhere in the forum. (Carb cleaner cleans the MAF, Brake cleaner removes carb cleaner residue)
