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Matt
Matt, Mechanical Engineer
Category: BMW
Satisfied Customers: 22255
Experience:  BEng hons Mech engineering, in auto industry 22 years
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Hi There, We live in France with our 2003 bmw 735. On a few

Resolved Question:

Hi There, We live in France with our 2003 bmw 735. On a few occasions last summer on hot days the car would be fine to drive in the morning, but come about 4/5pm the gear lights would flash on the dashboard and say failsafe mode not allowing any gear to be selected( Engine always starts). By the next morning it would again be fine. No problems over the winter. But now it has started to warm up again the problem has started again. I can drive around stopping and starting car all morning with no problems but around 5pm at the hottest time of the day the same message appears and the car will not move, along with airbag/ seatbelt light on. Our French bmw garage has never seen this problem before and I fear may charge us a great deal without fixing the problem. Any suggestions would be much appreciated .
Submitted: 4 years ago.
Category: BMW
Expert:  Matt replied 4 years ago.

Hello


This could be a wiring issue as things tend to expand when hot and its possible a poor or partial electrical connection is being pushed apart on one of the major sensors so check the connection plug and wiring to the following;

Airflow meter

Crank position sensor

Cam position sensor

O2 sensor

Throttle position sensor

also do the same for the gearbox electrical connections

Also worth checking the connections to the fuel pump for the same reason - unplug each in turn and give them a good squirt of switch / contact cleaner - Not WD40

and also unplug and inspect the main power relays and fuses for signs of overheating or corroded terminals - so the ones for the ECU and the fuel pump

And also unplug the wiring loom connections in the engine bay one at time and inspect for corroded or recessed pins.


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