ECM Code 25

[mrjoecanadian]

I put my code tester on for the first time today and I got code 25 and 27.

25: Manifold air temperature (MAT) sensor - signal voltage is low or high
:Vacuum switching valve circuit open or shorted to ground

:ATS sensor - signal voltage is high or low

27: 2nd gear switch problem

Okay so error 25 is the one that I thing is giving me my pore fuel millage but I don't know where to start changing sensors with that it is very vague in the code reader book. Any help would be apricated.

And if anyone knows anything about either code problem let me know what you did and how to fix please.

oh yea and pictures help thanks. My Haynes Repair Manual sucks.

[mrjoecanadian]

ok I looked up some more and in my Haynes Repair Manual for error 25

the manual has

MAT sensor or circuit - hight temperature indicated (1990 and earlier models)

IAT sensor or circuit - hight temperature indicated (1991 and later models)

So I am guessing IAT where is this sensor?
Picture would be nice
thanks for any help.

[mrjoecanadian]

ok so no help, I can't even find the IAT on my car :mad:

[pokesmot]

our 3.3's dont have a IAT (idle air temp) sensor.

I checked my GM service manual and there is no listing for code 25... are you 100% sure its 25?

I'm willing to bet its code 26 accompanied by code 27.

code 27 is a second gear switch fault, I have yet to fix this problem myself after tearing the valve body on the tranny apart replacing the TCC and all switchs... im pretty sure its a bad ground on the valve body :mad:
(btw code 27 will NOT illuminate the check engine light)


code 26 is a quad driver module (QDM) fault. Quad driver modules are basically switchs that are controlled by the ECM. the ECM closes the switchs by grounding certain circuits, code 26 comes on when something reads open when it should read closed or vica versa (your second gear switch)

aside from taking the valve body on the tranny apart and replacing everything theres no real way to fix the 26, 27 code faults :(

Like I said, I replaced everything, but never bothered testing it because I assumed the new stuff was all good, never figured id have a ground problem. If you do go ahead and do this, make sure you find a way to run a ground wire to the second gear switch.

[mrjoecanadian]

I'll throw my code reader on it today as well.