C4 Code H74

[ramrod]

I recently noticed the SES light come on itermittently ( 93 Convertible - Automatic ) ...I shorted pins A & G on the ALDL and the Speedo displays a code
H32 for module 4 ( I believe this is an PCM code for an EGR issue ), I then see a code H74 for Module 1 ( I believe this is the CCM ) ...I cannot find any reference for a code H74 on Module 1 ...anyone have any ideas ?

In the reference material ( http://www.c4vettes.com/ecm.htm ) I am looking at, the 1st suggested step for the H32 code is replacement of the EGR switch ...does this sound right ...has anyone done this and if so is it fairly easy to get to ?

I'm stumped on the H74 !

 

[Gorgon]

You are correct on DTC 32, this is the EGR code.

DTC 74 is Traction Control System circuit low. This is from the 1995 Helm manual. If you need any more info on these codes, let me know. I'm sure vigman or someone will pop in with some good info.

Leon

 

[ramrod]

Code 74

Thanks for info on Code 74 ...any info on cause of this or possible cure ?

 

[Gorgon]

It seems the PCM receives a signal from the TCS (Traction Control Circui). When a the TCS system is engaged the voltage is pulled to zero volts. This code will set if the car is in park or neutral and the TCS/ASR active signal input is zero volts for more than two seconds.

There could be a short to ground causing this or if it is intermittent, it could be a loose connector on the PCM.

DTC 74 will clear if the condition goes away and the ignition switch is cycled. The H in your code denotes a history code. Without a scan tool you will not see if the code is being set in real time. You can try to clear the code and see if it's still being set.

Leon

 

[ramrod]

DTC 74

Thank you for the info ...I assume that if the SES light is not currently lit, the condition has cleared ...correct?

Anyhow, I have had the vehicle only a few months ...I drove it back to VA from FL. ...on the way back when I stopped at a rest stop I did cycle the anti-spin button a few times ...don't recall doing this while moving though.

Anyhow, the SES light currently is off. Is there any way to tell is anti-spin feature is working - short of flooring it from a stop

Thanks again !

 

[Gorgon]

Not sure. There is a decent section on TCS diagnosis in the manual, I would have to dive into it a bit. Like you, I have only had my car for a short time, end of July to be exact. So I'm pretty new to this machine. There are a couple C4 electrical gurus here that will probably be able to help you a little better with diagnosis and fixing the issue. Sorry, but I'm still a newb myself with this.

BTW, don't you just love the car? Where in FL did you go to pick it up?

Leon

 

[ramrod]

Clearing Codes

I just discovered that it is possible to clear all the stored codes using the DIC ( Driver Info Center ) buttons instead of removing the negative terminal on the battery ...what a great feature .

I'm still learning ...

 

[trackitman]

CCM H74

I have the same code on my '92.

CCM 1 H74

I have a shop manual, it states "Code 74 LED Dimming Output Circuit (Circuit open or shorted to ground).

I scanned the page. Let me know if you can read it.

Keep us posted on what you find out, I have not had the time to look into.

I also have H43 on the ECM (Knock Sensor), and H35 on the ABS/ASR, which is LRear Sensor.

 

[ramrod]

Code 74

Trackitman ...thanks for post ...I was able to read the page fine ...looks like this is not a Traction problem code ....sounds like a problem in the automatic light sensor.

Guess I need to check if my lights Auto-Dim ...

There is an ECM code 74 on 94 and later Vettes that is traction related, however, my Vette is a 93 and my code is from "Computer 1" ( I believe that is the CCM versus ECM ( computer 4 ) ) ...your page agrees with a code lookup I found in ALLDATA which I recently subscribed to ..