[EnclaveTorqued]

Desperate here. A very disruptive problem. ANY HELP / IDEAS will be helpful. Electrical schematic - or at a minimum ther START circuit electrical diagram would be helpfu

THE PROBLEM: For a couple of years, Occasionally (incidents could be a week or up to three months apart - with NO apparent situational relationship), turn key to "START" results in NOTHING happening. No perceptible audible click, NOTHING. Everything appears normal and correct. When key is turned to "ON", dash lights up, gauges cycle, and all warning symbols are lighted and indicators appear normal. Turning key from "ON" to "START", dash acts SAME as when normal starting, but NOTHING. Removing / reinserting ignition Key, Wiggling switch or flipping back and forth from ON to START - does NOTHING. Moving gear selector in / out of park - neutral makes no difference. Brake switch releases Gear selector and acts proper. NO OBDII codes at all.

After an indeterminate period of time (could be minutes - or DAYS after being towed home), car will start perfectly. Time differs enough you can't know whether to wait it out or if you are totally stranded and have to be towed.

IMPORTANT CLUES:
1). Most important! Nine months ago - a new symptom appeared (RAPID FLASHING CEL) when key was turned to Start. Starter and Start Relay tested good. Diagnosed (correctly) as Failed ECU. Torque Pro reported Network Communications Error. Main ECU fuse would blow as soon as ignition was turned to "START". Took 3 months to get a new ECU and finally obtained New (aftermarket) ECU. Keys correctly relearned and cured THAT failure, and everything_ worked perfectly. No OBDII codes and all OBDII readings (fuel trims, fuel-air ratio, emissions, cats - all well within factory spec.

2).. As part of the above incident - New Battery, checked ALL fuses in the fuse box, cleaned (with spray contact cleaner) ECU plugs. Wiggled ALL harness wiring and harness wires/plugs around the engine compartment and behind engine. NEVER identified anything that seemed to be possible issue.

THE PROBLEM:

I felt certain I had corrected an intermittent / failing ECU and fixed the problem. BUT the car has TWICE exhibited the same NO START symptom again - that went away by itself (once after a few minutes - once after 24 hours).

I am at a loss where to look without a schematic to identify possible TEST points. Any help or ideas would be greatly appreciated.

Sorry for the long post - but these intermittent ones are long drawn out problems!

 

[EnclaveTorqued]

ADDITIONAL 'THEORY' / UPDATE

Reading / studying / sleeping on the problem has surfaced an additional 'possibility' for which additional input might be helpful.

FACT: The 'ignition keys' (Not the FOB, the mechanical keys themselves) contain an imbedded passive microchip - similar to a Pet's MicroChip. This chip emits a 'unique' code when 'polled' that identifies the key and prevents lock picking or key duplication. When mechanical ignition key is turned "ON", electronics (locked somewhere - I know not where) polls the microchip in the KEY and sends it's "ID" to the ECU. If the ECU's stored copy matches, the ECU will - subject to other checks - command the Start Relay to activate.

POSSIBILITY: Radio Frequency 'stuff', in everything from transistor radios to quantum computers can do 'squirrely' things under odd conditions - such as different metals nearby, temperature extremes, etc. IS IT PLAUSIBLE that the Key Microchip is not being read correctly by the receiver (where ever it is), and thus intermittently sending a BAD "ID" to the ECU? (Seems to me a possibility).

QUESTION(s): 1.) If anyone knows, WHERE is the 'receiver' physically located?
2.) What is the standard reaction produced if the ECM sees an incorrect KEY has been inserted and "turned on"? Should that just 'quietly' prevent starting action as would be the case if someone inserted a wrong cut key blank as is happening in my case? OR -
3.) Should it activate the PATS alarm system?

Thanks in advance for any additional knowledge here.

 

[JayS]

That's a pretty crazy one and unfortunately I have nothing really to add. You might want to cross post this over on the Acadia forum. Far more Acadias on the road than Enclaves and more them are DIYers so it's a more active community.

 

[Butane]

Worth a shot to check the harness connections under the fuse box. The two screws holding the fuse box down are touchy. Turn a little to much and they're loose again. There was a bulletin issued for the problem, tape or some type of sticky padding is secured under the fuse box to maintain a good connection.

Personal experience, a few times I had the same no start/crank conditions. Pushing down on the fuse box fixed the problem.

Good luck either way.