James, I have a 1988 Corvette Tuned Port Injection (TPI) that randomly sets a code 36: a mass airflow (MAF) sensor function fault. I have replaced the Electronic Control Module (ECM), the mass airflow sensor, mass airflow sensor relay and the mass airflow sensor burn-off relay. I have also gone through the scan diagnostics and the diagnostic aids with no resolution.
Most times I can start the car cold and drive without a code, then when I shut off the car and restart it the code will appear right away or shortly after. Your help and advice would be greatly welcomed.
Mike, this is not an uncommon problem, fault code 36 is for the burn-off function of the mass airflow sensor.
My first question is are you using an oiled type air filter on the vehicle? If so, the first thing I would do is remove this filter and install a stock filter, clear the fault code and see if the fault returns. I have seen these oiled type air filters not cleaned correctly or over-oiled after cleaning.
If the air filter is not the problem the most common cause for this fault code is one of the two relays. When checking these relays make sure there are no burned or melted areas where they are connected.
Another common failure is the Electronic Control Module (ECM) with part number 1227165. If your ECM has this part number it possibly could be faulty. Before replacing the ECM check for any other problems.
How the System Works
After the engine has been running for approximately 15 minutes and then you shut the engine off, the oil pressure drops, which de-energize the mass airflow sensor power relay.
Shortly after that occurs the Electronic Control Module sends a ground to the mass airflow sensor burn-off relay that energizes the relay.
This closes the switch, which applies 12 volts to the burn-off relay.
At the same time 12 volts is also applied to the mass airflow sensor power relay and then power is sent to the sensor.
Visual System Test
After driving the vehicle for a minimum of a 10 minutes, when you shut the vehicle off the burn-off function will enable. Twelve volts will be sent to the hot wire sensing element making it glow red to “burn off” any contamination that may be stuck to the wire.
You can test this function in a few different ways. The method that requires no tools or energizing the relays is simple:
Expose the mass airflow sensor in the airbox where you can easily view it while the sensor is still hooked up.
Let the vehicle idle for approximately 15 minutes.
Have someone shut off the engine while you are looking inside the airbox at the mass airflow sensor.
You should see the wire in the center of the mass airflow sensor glow red within a couple of minutes of the engine being shut off.
If the mass airflow sensor does not glow red within a couple of minutes of the engine being shut off check to see if the relays are applying voltage to the mass air flow sensor. These two wires are easily seen in a wiring diagram of the vehicle.
Mike, your wire color should be dark blue and the purple. Check to see if these wires have 12 volts at the mass air flow sensor using a multimeter. This voltage will only be applied for approximately 5 to 30 seconds after the engine has been shut off after running for roughly 15 minutes. Note these wire colors may vary for the year, make and model of the vehicle you are working on. Check your service manual to ensure you are working with the correct wires.
If voltage is not present or only present for an instant, I would check the grounding circuit to make sure that the ground to the burn-off relay is constant. I have seen several problems with this grounding circuit not making a good ground. Also check to see if the relays are getting voltage, ground and a signal from the ECM.
Mike, if everything checks out good I have also seen the wiring broken internally where the mass airflow sensor plugs into the wiring harness. You can usually pull on the wires one at a time and if any of the wires feels elastic, like a rubber band, use your multimeter to check for an open circuit. There is an aftermarket repair pigtail for this problem. Well, I hope this helps. Good luck and let me know what the problem was.
Photography by James Berry