Sunday, Oct 18, 2015 at 19:00
I have been told the same thing (unable to find a previous fault that is not currently present) by a diagnostic mechanic.
A mates Falcon wagon stopped dead several years ago, and he called me, as
well as a mobile mechanic, because he was only 3kms away when the Falcon stopped.
When the mobile mechanic arrived (at the same time as me), he pulled off the fuel line, checked the fuel was being pumped under pressure, reconnected the line - and the Falcon promptly started and ran like a top.
When the mechanic was asked if he could now find the fault, he reckoned it was impossible, as no fault was now showing, and it was almost certainly a transient fault, probably caused by the ECU processor failing temporarily due to heat.
When the microprocesser chucks it in - then starts working again - there's no fault recorded. I had this happen on a Ford climate control ECU.
If the fault is intermittent or transient, and not occurring when its connected to the diagnostic computer, there's often a low chance of a diagnostic computer finding the problem.
Not all faults are stored in ECU logs, it depends on how the ECU is programmed at the factory.
I had a Falcon Ghia wagon once, and the Ford service manager told me how Ford had to readjust the engine ECU error code programming so that it did not record transient, unimportant faults, typically such as, a wayward stick hitting a wiring connector, and making that connector disengage momentarily.
The fault had to be recorded for more than few seconds on the Fords before it was logged.
In addition, silicon chips and microprocessors often fail due to heat and age - but they will start working faultlessly again, when they cool.
A tow-truck mate told me they NEVER tried to start any car that had stopped with an electronic fault.
If they did, they quite often started again (because the ECU or microprocessor had cooled), and the potential tow job promptly thanked them, and then drove off!! LOL
So .. they woke up to this stunt, and they always winched on the non-functioning vehicle WITHOUT attempting to start it - then, when they got to the delivery location, they would start it up, and drive it off the truck! LOL
Cheers, Ron.
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