Corvette Trouble Codes: Identifying and Solving the Problems

The relays changed in late '87. Relay No. 14089936 operated the MAF power, burn-off, and fuel pump. Although not always accurate, the connectors for the 9936 relay are the gray connector for the burn-off circuit and the black connector for the MAF power circuit. You'll notice that the new connectors are weather pack connectors to seal out moisture.

To check that the MAF burn-off is getting power, look for 12 volts at the MAF connector position E.

If you get a Code 36, MAF burn-off malfunction, it should immediately reveal itself at startup and it won't affect performance. '85 Corvettes will never show a Code 36, only '86-'89 Corvettes. You can check to see if the ECM is calling for an MAF burn-off by running the car for at least 5 minutes, and checking the black wire at connection F (circuit 900) on the gray connector. It should be grounded for approximately 30 seconds. This is the ECM grounding the wire to actuate the relay. If there is no ground, the ECM is at fault. If you have ground, check the power to the relay. If the relay is sending power to the MAF, check that the dark blue wire (position D) on the MAF sensor connector has power.

Chris has spent some time adding wires, meters, test lights, and jumpers, chasing down several specific reasons why Codes 34 and 33 will appear. Here is what he found: The dark green wire from the ECM to the MAF (circuit 998) can short to ground or short together with circuit 450 (black or black/white) and cause a Code 34. To get a Code 33, circuits 998 or 450 could have an open circuit. Recently, Chris has seen a few cars for which the only cure was to run new wires for both circuits. This cured the intermittent codes immediately.

Checking The Minimum Idle Air: The first step in checking the minimum idle air is to put the car into Field Service Test Mode. Do this by putting a spade connector into the A and B positions of the ALDL connector. With the key on and the engine off, the fan will turn on and the SES light will flash. Also, the Idle Air Controller (IAC) will fully close.