Holden Astra TS 2001 Z18XE


Engine fault light on and trasmission stuck in 3 gear
The client had dropped of the vehicle for diagnostics and we deicided to test drive the vehicle to confirm the symptoms, we found that the engine light and the service vehicle soon light is on.


We used the Bosch KTS scan tool to diagnose all the system faults with the vehicle and the faults came back with P100, air flow meter in the Engine ECU and a C0256, engine torque reduction malfunction in the transmission, this vehicle is an OBD2 Compliant vehicle and the fault codes are looked up from the OBD2 database table.
The clearing of the fault codes was not a success, after start up the fault codes came back, we used the current data/live data to check the output of the air flow meter and it read 0 kg/m
The air flow meter was obviously not working, so manual testing of the sensor had to be undertaken.
The wiring diagram shows the 3 wires connecting to the air flow meter, there is:
  1. Power feed to turn the sensor on (red)
  2. Output signal to Engine ECU (green)
  3. Ground. (Yellow)
  4. Intake Temperature Sensor Output (grey)
Simple testing on these circuits with a picoscope occilliscope revealed that the power feed is reading 12v, and that the ground was good. The output power was at 0 volts.
The airflow meter was changed with a known good unit, once the good unit was installed the diagnostics was not complete until we had check that the output signal was good, the output circuit now read at idle 1.2 volts and went up and down with engine speed, which confirmed that the sensor was doing what it was supposed to. The next step was to clear the faults codes in the engine ECU and Transmission ECU and take the vehicle for a test drive.


The vehicle was back to normal, with out testing the circuit with a scope we would not has been able to know for certain that the output circuit was faulted, we has tested many airflow meters on these vehicle and a very common issue is the Engine ECU, which drops out the Ground circuit.
It is very important to save time and carry out testing on sensors to give them a fail or Pass in order to move to the next step in diagnostics.