The problem

A Proton Impian was suffering from intermittent starting problems, and the vehicle randomly cut out. This caused the engine warning light to illuminate.

The first stage of the investigation was to use a diagnostic tool and obtain any 'DTC' (Diagnostic Trouble Codes) information and relevant data from the ECU. However, when this was tried, there was no communication with the scan tool. At this point it was unknown whether the scan tool or the ECU of the vehicle was at fault.

The CAN test box was plugged into the vehicle's diagnostic port, and the CAN High and CAN Low pins illuminated, indicating power from the ECU to the diagnostic port. At this stage the scan tool was plugged into the CAN test box. Still there was no communication, no K-line activity. This implies a fault on the scan tool lead, or communication key. Further investigation revealed the scan tool lead had a dirty connection on the communication key.

The diagnosis

Once the connection of the communication key was cleaned, it was possible to extract the DTC codes from the vehicle:

P0340 - CAMSHAFT POSITION SENSOR CIRCUIT 'A' BANK 1 OR SINGLE CIRCUIT

The DTC was cleared, and all tools disconnected from the vehicle. A road test was performed. On return to the garage and with the engine still running the cam sensor was scoped, as you can see in the waveform below.

The engine was then switched off, and would not re-start. The CAN test box and scan tool were connected to the vehicle via the diagnostic port, and the same DTC was extracted as before. The Camshaft sensor was then scoped, and the below waveform recorded.

This revealed the Camshaft sensor was at fault.

The repair

The faulty Camshaft sensor was replaced. The DTC was cleared, the car was started, and the new cam sensor was scoped.

A road test was then completed. On return to the garage the ECU was checked for DTCs and none were found.

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