I pulled the codes the other day off of my 95, w/ZF6 Does anyone know what H71, H72 mean at autozone they told me it was the temp sensor, and with previous help the 71 meant drivetrain "slippage" but no explaination for the 72. Any help appreciated I want a second opinion before I jump in to fix it.

 

damn... I don't have codes for a 95.

You really need to get a helms manual. www.helminc.com

They publish the GM factory service manuals. Each code is outlined and trouble shooting is given.

 

does anyone have a manual for a 95, or willing to sell one, I don't really have $130 for one.

 

this is one book where paying with a credit card is a good idea.

also, you can check ebay.

The value of this book transends its cost.

 

If SYS was flashing in the Instrument cluster LCD area it indicates a CCM error (Central Control Module).

If Service engine Soon was flashing in the DIC (Driver Information Center) it indicates a PCM error (Power train Control Module).

I'm guessing the error was a SYS error because there is no error code 71 for the PCM.

DTC 71 and DTC 72 (Diagnostic Trouble Code) are both error codes for the LCD Dimming circuit for the Radio Control head and the C68 (Auto Climate Control head display).

H means the error code is a History code and no longer exists.

DTC 71 LCD Dimming Circuit Shorted to Battery Voltage or the CCM circuit is bad.

DTC 72 LCD Dimming Circuit Open or Shorted to ground.

Basically what happens is the CCM monitors the circuit.

1) Ignition is on
2)Head lamps or Parking lamps are on
3)The Dimmer on the Headlight switch is not set for 0% or 100%

DTC 71 sets because the CCM does not see the signal line go Hi over a certain time frame.

DTC 72 sets because the CCM sees the signal stay low for a certain time frame.

The manual says possible causes are bad connections at the CCM connector, Radio Control head connector or the connector on the back of the A/C Heater Control Head.

If you turn on the Head light switch and use the dimmer and the LCD backlight works, just clear the Codes by disconnecting the negative battery cable for a couple of seconds and reconnect it.

If you have an aftermarket radio, it can cause the CCM to set error code 72. If that's the case, the SYS light will continue to flash until you install a resistor in the Dimming control line to complete the circuit.

 

Try going to www.troublecodes.net. You'll need to know your vin number either J or P on the 8th position. I don't have the 71, but the 72 is : Transmission output speed changed more than 1000RPM for 2 seconds when the vehicle was in gear. or transmission output speed changed more that 2048 RPM when vehicle was in park or neutral. Hope this helps.

 

Yeah the sys has flashed before in the past so I think that might be an old problem, and the service engine light came on recently, so I think the two are seperate, is there any chance of the c beam bending to allow driveline flex, which then the change in rpm speed would then cause that error?

 

Say what?

 

I feel a flex in the driveline, and all four bolts are tight, is there a chance the C beam can weaken, and bend, causing the 2000 change in rpm code to be set off?

 

I just recently had a new CD head unit installed in my 1992 Corvette. Where can I find details on installing the resistor to keep the SYS warning from flashing?

 

I'm getting the same code (72) happen right after I replace the stock stereo with an aftermaket. I would also like to know how or where to jump the dimer or whatsize resistor. THis is driving me CRAZY>