Check Engine Code #26-Quad Driver 4
Thread Starter
1st Gear
Joined: May 2011
Posts: 1
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Check Engine Code #26-Quad Driver 4
I have a 1992 corvette. The check engine light came on and the diagnosis was Code #26-Quad Driver 4. I sent the computer to be repaired and upon receiving it, it still had the same code. After 3 attempts, the company sent me a new computer. It still says the same code. I had a GM certified mechanic check the wires going into and out of the computer and he found no problems. Any one else have this problem? If so- what fixed it?
Melting Slicks
Joined: Aug 1999
Posts: 2,240
Likes: 41
From: Baltimore, MD USA
I believe 92 and 93 Vin P Corvettes used the same ECM. This information is from a 93 manual which says DTC 26 is Quad Driver #1 circuit. You say DTC 26 Quad Driver 4?
ECM DTC 26 indicates a problem with one of the following circuits.
1) Evap canister purge solenoid
2) EGR solenoid valve
3) Air pump relay
4) Air bypass solenoid valve
The ECM monitors the voltage and current to determine if
there is a problem with any of the 4 circuits.
On the ECM Gray colored connector
Pin A1 Dark Green/Yellow wire is for the Evap canister purge solenoid
Pin A2 Gray wire is for the EGR solenoid valve
Pin A7 Brown wire for the Air pump relay
Pin A8 Black/Pink wire for the Air bypass solenoid
A GM tech would use a TECH 1 tester to turn on each solenoid or relay
and verify the ECM detects the proper voltage. The current draw for the
relay or solenoid should also not exceed .75 amps.
If either the voltage or current measurement is not correct for
20 seconds, DTC 26 is set.
The chart lists a method to test each circuit using a Digital volt meter.
You can disconnect the Gray plug at the ECM. Set the meter to read
at least 2 amps of current. One circuit at a time you place the red probe on each pin and the black probe to ground. Turn the ignition On.
Each relay/solenoid should energize. The current flow should not exceed
.75 amps.
ECM DTC 26 indicates a problem with one of the following circuits.
1) Evap canister purge solenoid
2) EGR solenoid valve
3) Air pump relay
4) Air bypass solenoid valve
The ECM monitors the voltage and current to determine if
there is a problem with any of the 4 circuits.
On the ECM Gray colored connector
Pin A1 Dark Green/Yellow wire is for the Evap canister purge solenoid
Pin A2 Gray wire is for the EGR solenoid valve
Pin A7 Brown wire for the Air pump relay
Pin A8 Black/Pink wire for the Air bypass solenoid
A GM tech would use a TECH 1 tester to turn on each solenoid or relay
and verify the ECM detects the proper voltage. The current draw for the
relay or solenoid should also not exceed .75 amps.
If either the voltage or current measurement is not correct for
20 seconds, DTC 26 is set.
The chart lists a method to test each circuit using a Digital volt meter.
You can disconnect the Gray plug at the ECM. Set the meter to read
at least 2 amps of current. One circuit at a time you place the red probe on each pin and the black probe to ground. Turn the ignition On.
Each relay/solenoid should energize. The current flow should not exceed
.75 amps.
Last edited by Hooked on Vettes; May 12, 2011 at 11:07 PM.
Safety Car
Joined: Jun 2006
Posts: 3,629
Likes: 28
From: FL
If the GM "certified" tech mentioned advised you to replace the ECM based on the code without following the troubleshooting chart in the FSM I would avoid him in the future.
The EGR and EVAP solenoids are common failure items that can cause this code. A quick test is to check resistance across the two pins of the solenoids with an ohmmeter, a bad one will be "open" = infinite resistance.
The solenoids are located under the fuel rail covers,canister purge EVAP, on the right side shown here (red and blue connector):
EGR under left fuel rail cover shown here "blue connector":
To remove the fuel rail covers simply lift straight up.
