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Matt
Matt, Engineer
Category: GMC
Satisfied Customers: 21973
Experience:  Honors degree in Mechanical Engineering, worked 8 years as a Formula 1 engine engineer.
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My car won't crank, completely dead. Full tank. At first it

Customer Question

My car won't crank, completely dead.
JA: Have you checked the fuel supply? And are all the spark plugs working?
Customer: Full tank. At first it would not crank then when driving, the radio reset on its own. When in the drive way and put in park, i turned off the car and now it's completely dead. Can't even jump.
JA: What is the model/year of your GMC?
Customer: 2013 Denali Yukon
JA: Are you fixing your Yukon yourself? What have you tried so far?
Customer: AAA is trying to jump it
JA: Anything else you want the mechanic to know before I connect you?
Customer: The battery and alternator was replaced a month ago.
Submitted: 2 months ago.
Category: GMC
Expert:  Matt replied 2 months ago.

Hello

If the car's not cranking then first check it can turned over by hand by using a socket on the crank pulley nut, so double checking for any mechanical issues

If OK then check that the main battery cables are on tight and the terminals are clean and bright. Do the same for the engine / gearbox earth strap.

Then follow the main positive lead back to the engine and down to the starter motor, and check the connection at this end as well.

There should also be a small wire to the motor which should have 12V when you're turning the ignition switch / pushing the start button to crank. If the 12V isn't there, check back along this wire for damage to the insulation or corroded connections

This 12V feed comes directly from the ignition switch / starter button so this may be faulty and need replacing

Check the resistance of the main positive lead that runs down to the motor as anything more than a few ohms and it should be replaced

Don't forget to try a jump start from another car / battery as its possible the battery is poor, if you have a voltmeter a healthy battery should read 12.7+V

also try substituting the battery for another as I've known a very flat battery to drag down the system voltage too far even with jump cables

one other thing to consider is that the immobiliser is faulty and preventing the starter from being enabled - however if the dash / ignition lights are on then this usually means that its off

If this is all OK then its possible the car needs a new starter motor

Customer: replied 2 months ago.
Triple A seems to think it may be the anti theft system.
Expert:  Matt replied 2 months ago.

Hello

if the lights on the dash aren't coming on then I'd agree that this is likely to be the security system

if you measure for 12V on the ECU fuse and if its not present then this is another confirmation

in which case the next step would be to disconnect the battery and charge it up overnight then reconnect it and try again in the morning

if that doesn't help then I'm sorry to say that you'll need to get the car to the dealership as only they carry the correct kit to recode the security system to the key

Customer: replied 2 months ago.
It finally cranked and he said he believes that it is the anti theft system
Expert:  Matt replied 2 months ago.

If its cranking / turning over then the security system may no tbe at fualt as it should cut both the starter and the ignition

check to see if you have 12V on the ECM fuse next

if you do then

1st check for spark by removing one of the spark plugs and plug it back into its lead and rest it on the metal of the engine ( DO NOT hold it on place by hand) then have your assistant turn the engine over whilst you watch the plug. It should give a fat blue spark at regular intervals.

If not then check that there's power to the coil pack (at the other end of the plug lead) using a meter. If there’s 12V at the pack but no spark then check the ECU power supply (fuse and relay) and also the connections to the crankshaft speed sensor.

If you can't hear anything check the ECU power is present by measuring voltage at the fusebox and on its relay socket if OK then check the connections to the crank speed sensor and consider replacing this sensor if the wiring / connections look OK

If the car will start using a squirt of quick/ easi start into the intake then this confirms the problem is lack of fuel

Also its worth checking that the electric pump that feeds the injectors is working correctly, it should run for a few seconds then switch off when you first turn the ignition on. If you remove the filler cap to the fuel tank and listen inside while your assistant flicks the ignition you should hear it clearly
If the connections to this are corroded or damaged then the pump could stop at any time. Check that its relay switches in and out and the relay contacts are clean and bright – replace the relay if in any doubt and do the same for the fuse, ideally measure the voltage at the pump and check its getting 12V.
You should be getting around 3 bar measured at the injector rail check to see if the plugs are getting wet indicating fuel is flowing – if not and the injectors are opening then there’s a problem with the pump or the filter or even the pressure regulator

Expert:  Matt replied 2 months ago.

Hi
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