Troubleshooting
This diagnostic article takes you through the process the AECS technical support team use with problematic vehicles. We look at the issues involved and share how we assisted in resolving the problem. This an inside look, from the profound to everyday issues automotive workshops encounter.
A BMW 2001 528i had been intermittently not starting. It would only very occasionally fault. The starter had been removed/inspected/tested with no issues noted which is surprising for such an old vehicle.
The spare key had also been used for a period to rule out key transponder issues.
After several fails a fault code was recorded in the engine control unit DME. This fault code indicated a communication issue between the engine control module and the immobiliser unit EWS.
Lost confidence
Not surprising, the owner had lost confidence in the vehicle after he had several long waits to be able to start the vehicle, and also long walks home or to appointments in frustration.
Measurements
We guided the technician to a wiring diagram pin out in his
ATIS system which is part of the ATS scope software to find the communication line between DME (engine ECU) and EWS (immobiliser) control units. He left a probe in place with he scope in recording mode to capture the signal as soon as the failure occurs. He also mapped out and recorded the EWS module pins for all voltages and signals so this could be used when the failure occurred. The plan is based around finding the corrupted/missing signal. Now it is simply a matter of regular starting until failure occurs while being ready to carry out measurements.
We can see in the recording that the EWS controller does not send out its signal when it is supposed to. Once key is inserted it should start sending a drive authorisation signal to the DME. All wires at the EWS were subsequently tested and compared during the next failure to ensure that it was getting all the correct signals and power supplies. All voltages and signals were exactly as they were when the car did start.
A replacement EWS immobiliser controller was ordered and installed. The new unit required chassis number writing into it and synchronisation of signals between EWS and DME units. This was carried out with Launch Auscan3 scan tool.
Closing
The technician showed the owner how the diagnostic strategy was applied, sharing screen shot recordings. The bill was paid without hesitation. The vehicles owner was extremely happy to now have the option of driving without the worry of needing walking shoes as a backup plan joking that he was becoming like Tom Hanks in the movie Forrest Gump.
This is a job where a scan tool would take you halfway. Is the fault power supply, earth, wiring, engine ecu or immobiliser? Without an oscilloscope and AECS support you have no way of knowing. Every repairer owns a scan tool. Why is this not complimented in every workshop by a quality recording oscilloscope?
It is not that this job was a late model rare car! Jobs like this should be almost as normal as everyday oil changes.
Following on from the two-part brake tester articles in the previous two issues there has been quite a bit of feedback, We have provided an update on our website focussing on an Australian report (Aecs.net) for those who want to learn more https://aecs.net/techniek2021/AECSTechnics_Update1_Apr21.pdf (Or https://tinyurl.com/bha78c58 to save typing!)