Greetings all,

Recently picked up a 95 coupe and am waiting on a set of manuals I recently ordered. But while waiting I'm trying to troubleshoot an ongoing sys flashing and a code H25 being set in the CCM. I think I've eliminated a low battery issue and the car has the original BOSE stereo.

Code 25 indicates the intake air temp sensor circuit voltage is low. I have checked the thermistor sensor and it reads about 2.5K ohm at room temp and about 400 ohms shortly after removal from the car when hot. Again I'm waiting on my manual set so I'm not sure what this sensor is suppose to be reading. Also I'm not 100% sure which sensor the intake air temp sensor is. I'm presuming it's the one located on the passengers side of the air intake "hose"???

If I reset the CCM and check it again after idleing in the driveway it does not set another code. However within a block or two of driving the sys light is flashing again and when I get back and check I have a H25 code again.

Any thoughts would be greatly appreciated!

TIA.

 

As a followup to the above post, here's a pic of the intake runner. I'm presuming that the intake air temp sensor is #1. Once again while waiting on my manual set to arrive, what sensors/devices are #2 and #3?





TIA!

 

IAT sensor is #1 in your photo. You were correct.

Your posting the battery and Boes info was also helpful.

I don't think my FSM says what the IAT resistance should be at different temps. It says that checking it against the ECT on a cold engine should show them in agreement. You will need a scanner (not simple code reader) to perform that check. I would be glad to check the resistance of the sensor on my '94 and send you the temp and resistance if you wish.

#2 IAC Idle air controler
#3 TPS Throttle position sensor

 

Thanks for the offer to measure your sensor, but I was able to get a copy of the DTC25 pages from the FSM which indicates the resistance at various temps. See the next post as to where I'm at now.

Thanks again!

 

Thanks to the kind offer from a fellow vette owner, I was able to get a couple fsm pages relating to a DTC25 code. I now know that my IAT sensor appears to be working normally and producing the right resistances/signal, but the car still is setting a H25 code and flashing SYS too.

So next I took a fixed 1K resistor (the resistance indicated for an approx 120 degree signal and right in the middle of the correct temp range) and plugged it into the connector in place of the IAT. Reset everything and within a block the car threw another H25 IAT high temp/low voltage code again.

Once again I cleared the codes and then completely disconnected the IAT which should make it throw a low temp code. (H23) It did, but also threw the high temp code (H25) too. Gee, how can it be low and high at the same time???

Additional info is that the H25 codes comes up under module 1, the CCM. However the H23 code shows up in module 4, the PCM. I wonder why the opposite codes for the same sensor are showing in two different modules? And I'm also now wondering if perhaps the H25 in the CCM is trying to tell me something other than an IAT sensor issue. Sure seems that way at this moment.

So once again any input would be most welcome. The issue is probably something stupid, but at the moment it is being elusive and driving me a bit crazy too.

TIA!

 

Gee, no ideas from anyone? What happened to all the knowledge here?

 

I really do not know, but do not rule out the ecm.
I hope it is not that, but someone with more experience can chime in.