Intermittent no crank no start
I have an Intermittent no crank no start on a 2008 buick enclave, according to the customer these are the symptoms. Vehicle has not acted up since looking the vehicle over. battery tested and passed, charging system and starter also tested and passed. also no codes.
Vince Try doing a flood mode test to see if the starter acts up...
Have you studied a wiring diagram and the theory of operation for the starting system? Any volt drop testing of the starting circuits?
I would current ramp starter with your scope in clear flood mode . And see heath of the starter and circuit. And did you load check battery ???
No crank covers a lot of problems.....If the starter attempts to crank but does not have enough power to turn engine over could be open comm bar and when armature stops turning the open comm bar may stop on one of the brushes which would give you less torque & RPM's Ask customer if the solenoid makes a loud clicking sound ?
Customer said it didnt click nor crank at all.
I did load test battery & it passed its only 1 year old. also did a starter amperage draw test & it also passed. Going to try the flood test on starter.
loaded the battery with a carbon pile tester and it passed, battery is 1 yr old. also did a Amperage draw test on starter. will try the flood test on starter. ty
Engine compartment fuse box has three bolts that are usually overtighten and stripped. This causes intermittent engine/electrical issues with bad connection or damaged terminals.
This may seem “way out there” but I was called in to diagnose a Buick 3.6 of that era that had an intermittent no-crank but the shop could occasionally duplicate it and discovered no PCM communication with a scan tool when it wouldn’t start. they would jump the starter relay and it would then start and run normally and restart again normally with the key till it went through a cold soak. I…
I have seen the same thing on several vehicles with the Boshe pcm. Sometimes you can just momentarily touch the starter relay wiring at the pcm with a grounded test light and they will then crank from the switch.
Look for the grounds Around the engine bay that are loose or damaged. Try using a jumper cable, introducing a secondary ground to body and ground to engine.
don't touch anything until you get it to act up. Everything else is just a guess. Rule 1, duplicate customer complaint....
Vince, first test the power present on the starter 50 Terminal when you crank.if not check the starter relay there should be one ground and one power and power from starting switch (Ignition switch) (key). I would normally try to energise the starter first on this matter.
Check pins 6 and 14 at dlc for 60 ohms of resistance on the high speed network. Leave dvm hooked up for the next step. (I’ve seen the rear differential clutch wiring harness chafed in the left rear wheel well) Wiggle the rear diff clutch harness where the harness gets flat near the subframe in left rear wheel well. When this acts up it takes out the high speed network, no start no run.
This model is not AWD dont see a rear diff, or harness. but still will check the pins you mentioned ty.
Lot's of possibilities. Without symptoms present, any repairs will be a guessing game. I have seen sunroof leaks wetting the fuse panel above the passenger footwell cause a no start. Any signs of moisture inside?
When I load test a battery I do it in the customer condition for the no start. Example. It was -10 or lower in anchorage in January. We had a lot of people complaining that car would not crank. Other people in the shop would just do a carbon pile tester in the shop. A alternator, battery & starter test, the battery would pass. Parasitic draw test would pass. Customer would come back…