An interesting case came through the Helpline recently for a 1999 Volkswagen Golf 1.8i that had a misfire.

On initial investigation, one ignition signal was missing. The spark plugs, ignition coil and leads were replaced, but the misfire and signals remained the same. The primary circuit was load tested to the ECM, but no fault was found.

The ECM was then sent for testing and repair. Unfortunately, due to the age of the vehicle, the repairer could not test for the missing signal. The ECM was returned to the garage, and a new unit was the next step. Once again, the age of the vehicle was a problem, no new ECM was available. There were used units available, but they would require the immobiliser code to be programmed on the replacement ECM. This would require specialist equipment to complete this coding process.

We know the security for this ECM is in the binary code on an EEPROM 24C02, and a technician just needs to edit this code to allow the ECM swap to take place.

There were 2 options available, either desolder the original EEPROM and replace it into the used ECM, or read the binary file on the original EEPROM and write it back into the used ECM. We opted for the second option, and below are the 2 BIN files showing the differences in the immobilser coding.

All that was required to perform this task was an EEPROM programmer. For this case, we used an Xhorse VVDO PROG programmer, a generic chip programmer. This enables the EEPROM to read, edit and rewrite the files in circuit without demounting it from the PCB.

This can save a classic vehicle, allowing it to remain on the road for some time to come, without the expense of a new unit, which could make the repair not viable.

To see or download this article click here.

There are lots more Tech Tips to view, and they are all searchable, on TechTips.ie.

To join the Autobiz Helpline, call 01-905-9500, and then press 2, for further information.