I have a 1995 GMC one ton pickup with the 6.5-liter Diesel. I've been having all kinds of oddball problems, and recently had a garage check it for trouble codes. They came up with a 36, 62, 65, 78, and a 99. What do these codes mean, and what could the problem be?
The basic rule of thumb when dealing with multiple trouble codes stored in the Power Control Module's (PCM) memory is to clear the codes and see which return first. This tells us which codes represent the "hard failures" that may have instigated the others. Today's computers separate the "current" and "history" codes. This can indicate which failures are happening right now, and what failures occurred previously.
Trouble code 36 represents an "injection pulse width error". The injection pulse width is the "on-time" or the amount of time (measured in microseconds) that the "fuel solenoid" located on the electronic injection pump is open and allowing high pressure fuel delivery to each cylinder. A possible cause of a code 36 is a weak fuel solenoid, but a defective PCM or a poor electrical connection in a number of locations could also be at fault.
The fuel solenoid is non-serviceable and comes as part of a complete electronic injection pump replacement. Remember, we said this is a possible cause to the problem, not a definite fix. The system needs to be gone over by a qualified technician with the proper tools in order to be accurately diagnosed.
We had a related question pertaining to a Chevy 2500 Diesel pickup. This reader's truck appeared to be suffering from an intermittent failure of the "Optical or Pump Cam/Fuel Temperature Sensor" which also requires the complete replacement of the electronic injection pump.
Turbo boost sensor low, Code 65 is Accelerator Pedal Position No.3 fault, Code 78 is Wastegate solenoid fault, and Code 99 is Accelerator Pedal Position No.2 fault.
The Accelerator Pedal Position Sensors (APP) have problems along with the electronic injection pumps. This most certainly could be a multiple failure situation.