92 sc400 code 31

[sc400jonny]

hello i have some issues with my 92 sc400 giving me a code 31 and i have read the repair manual and it points to mostly replacing the ecu but before i do that would you guys give some advise on this situation?
also when i get on freeway speeds and don't let the throttle stay in one spot the engine light would go away and would drive normally don't know if that means something.
thanks

 

[P Bateman]

The repair manual can be prone to dramatics sometimes. If the ECU cannot determine the cause of the fault, it blames itself. I have seen plenty of ECU's replaced unnecessarily when techs only follow the DTC guide.

Start by removing the air flow meter connector and inspecting the terminals. Look for any corrosion, damaged wiring, bent pins, etc

Plug it back in and, with the ignition switched on, check the voltage between pins 4 & 5 on the air flow meter to make use it's got good power and ground - it should have 5volts.

Switch the ignition off and disconnect the air flow meter and ECU connector - check the resistance between Pin3 on the air flow meter and Pin66 on the ECU - it should be less than 1 ohm

When checking these wires:

• DO NOT front probe the connectors - always back probe, and don't damage the wiring insulation either. Insert a sewing pin into the back of the terminal
• Don't just test them in situe - wiggle them around and tug on the harness to ensure there isn't a poor connection when the engine is running/vehicle is moving.

Come back with your results.