With the help of "Hooked on Vettes" I pulled the following from my 1994 Z07 corvette:
1. C12 ---
4. H27---
9. ---
A ---
1.0

Help Please!

Thanks

 

27 is a problem with the EGR Vacuum control signal solenoid valve. The PCM monitors the voltage change at the solenoid.

The PCM controls the opening of the EGR valve by grounding the solenoid valve which will allow vacuum to be applied to the EGR valve.

The solenoid valve has a two wire connector going to it.
On a 95 the two wires are Pink which is 12 volts from the 10 amp ENG1 fuse located in the passenger side fuse box. It is hot when the ignition key is in run or start.

You need to open the passenger side door and remove the plastic cover which covers the fuse box and see if the fuse is good.

The other wire is Light Blue. The PCM grounds this wire to activate the solenoid. I'm not sure if the wire color coding is the same on a 94. I'm looking at a 95 manual.

So if you turn the ignition to run and manually ground the Light Blue wire, the solenoid valve should allow vacuum to pass to the EGR valve. If the solenoid valve does engage, the PCM may be bad.

To find the solenoid valve, trace the vacuum hose from the EGR valve. It should lead you to the solenoid valve.

 

I located the EGR Vacuum control signal solenoid valve. I see a pink and green wire(probably blue as you stated 95). So If I ground the green wire the EGR Valve will receive vacuum. To tell if it is receiving vacuum I will have to pull the hose and feel for vacuum or can I see the valve engage?. If it doesnt receive vacuum the EGR Vacuum control signal solenoid valve is bad?. If it does receive vacuum, it is possibly the PCM. Is there a way to further pin point it to the PCM. If it is the PCM, I will have to get a new ECM and have it programed. Correct? Thank You for your help!

 

Did you verify the 10 Amp. Eng 1 fuse is good?

To manually activate the Solenoid valve, the ignition must be in run (engine off) and you ground the Light Blue wire.

In normal operation.

When the PCM applies a ground to the Light Blue wire, the Solenoid valve activates and allows the vacuum to be applied to the EGR valve. The PCM monitors the voltage on the Light Blue wire.

When the Solenoid valve is not activated. The voltage on the Light Blue wire should measure around 12 volts.

When the Solenoid is activated the voltage on the Light Blue wire should measure close to 0 volts.

DTC 27 sets when the PCM detects the wrong voltage potential on the Light Blue wire for 20 seconds.

DTC 27 is only checking for the voltage on the Light Blue wire and not checking the vacuum part of the valve. (So don't worry about the vacuum part).

If you have an Ohm meter, disconnect the electrical connecter going to the Solenoid valve and see if you can measure the resistance of the Solenoid coil. It
should be around 25 ohms. A very low resistance could indicate a shorted coil and a reading of infinity would indicate an open coil.

The dealer would use a Tech1 or Tech2 to diagnose the problem. With that device that can activate the Solenoid Valve.

If you decide the PCM is bad, yes the new PCM needs to be programmed.

 

If memory serves me the "H" before the 27 or any code indicates it's a "history" code. Which means it was some time ago and the problem may not still exist or code wasn't cleared after repair was made. Try clearing it by disconnecting negative battery post for 30 seconds then re-connect it. This will clear all codes. Then run the car for a bit and see if SES light comes on. If it does, that means a code has been thrown. Even if it doesn't, pull the codes again and see if the 27 is still there. If so then fix it, if not it may be an old code thats been already repaired.

 

Pertains to 90-95 Vettes.

All ECM or PCM error codes are displayed by the CCM as History codes.

 

On a 1995 - you cannot clear codes by taking off battery terminal. This come stright from Gorden Kilibrew (I bought his code readers and it came with a book).