How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Pete Your Own Question
Pete
Pete, Auto Service Technician
Category: Chevy
Satisfied Customers: 27647
Experience:  14 years GM dealer Technician.
14928985
Type Your Chevy Question Here...
Pete is online now
A new question is answered every 9 seconds

I have a 2008 Tahoe Hybrid with 103k miles. I've been having

Customer Question

Good morning. My name is***** have a 2008 Tahoe Hybrid with 103k miles. I've been having problems with the car since roughly 95k miles. First problem I really noticed was a violent shaking when the car would slowly accelerate or decelerate around idle. Almost felt like the car was confused between hybrid and gas ignition. I've taken the car into my local Chevrolet dealership multiple times and they can't seem to find the problem. They have reset the computer multiple times hoping that will solve the problem. Unfortunately, the engine light doesn't come on when this happens. Another issue from this problem is causing the car to accelerate on it's own and RPM's will shoot up making me slam on the brakes.
The second issue I'm having (not sure if it's related to the 1st) - is the car will shut off while accelerating from idle. It will jump and then shut off. I can restart the car and it will turn over, but then it cuts off again when I'm at the next light. I've noticed the jump before when I accelerate from a dead stop, but when it cuts off I'm afraid someone will rear end me and with kids in the car this scares me. And when the car accelerates on it's own I'm nervous for my family as well. I took the car (again) into my dealership and (as the engine light finally came on when the car shut off on it's own) and they eventually found some code (wouldn't tell me what it meant) advising they made the engine light go away. I've taken my car into multiple mechanics with no one knowing what the problem is ... hoping someone can help me out. I'm at a loss. Thanks
Submitted: 11 months ago.
Category: Chevy
Expert:  Pete replied 10 months ago.

My name is ***** ***** I am a professional here at Just Answer. I noticed that your question had not received a response and thought I would see if you still need help with this.I apologize for the delay and I hope I can still assist you with this here.

I have seen issues on some models with the engine throttle body that can act up and cause this type of fault here needing replaced for this issue.If they did not check into this to see if this is the cause here this needs done to see if it needs replaced.I have had to ask customers of my own if I can hold onto their vehicle for a day or more so I could duplicate the fault to diagnose and repair it from there.

If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service,your 5 star rating is appreciated.You can rate at any time and we can continue to work on your question as this will not close out your question.Keep in mind in some cases it can be difficult to fully diagnose or help repair your vehicle without seeing it and I work on delivering the best possible answer from what I see to work with.

Thanks Pete

Customer: replied 10 months ago.
Thanks for the response, Pete. You were correct - no one had reached out yet. Unfortunately, I have already tried replacing the throttle body and that didn't solve the issue. And I have left my vehicle with the dealership for multiple days at a time. Any other suggestions? It's actually getting worse. Yesterday I drove with my kids and I would push the gas pedal only to have the car sit there ... raise RPMs and not go anywhere. I would have to let off the gas and try again - it would eventually catch and start moving but only after another hesitation.
Expert:  Pete replied 10 months ago.

Your welcome

Was the dealer able to duplicate the fault at all do you know?

Customer: replied 10 months ago.
Of course not. Murphy's law. But somehow from the last time I gave them my car for a few days and them driving it 80 miles (so they say) it has gotten worse
Expert:  Pete replied 10 months ago.

Do you have any after market wheels or components on your vehicle at all?

Expert:  Pete replied 10 months ago.

Incorrect sized tires?

Customer: replied 10 months ago.
No and no
Customer: replied 10 months ago.
All stock
Customer: replied 10 months ago.
Vin: 1GNFC13548R232792
Expert:  Pete replied 10 months ago.

There are some complaints and issues with the 12 volt battery being low voltage intermittently causing this issue here needing replaced.it may have checked/tested o.k. for them when they had the vehicle but this can cause this fault here.The throttle body is the main cause though and several complaints on this causing this fault here.It might be worth replacing since they cannot locate the fault and having the 12 volt battery and battery cables and connections checked.Below is the operating characteristics that are normal for this engine and if there are abnormal operations occuring that do not fit this below then I would check into the battery,cables and throttle body as one of these will be the cause here.

• Stall during shift out of park immediately following engine crank. This is a normal operating characteristic. Some drivers are able to interrupt the engine start sequence by shifting the transmission out of park. The ECM will turn off fuel and spark to the engine if it isn’t running and the transmission has been shifted out of park or neutral. Inform the customer to wait one to two seconds before shifting out of park or neutral to ensure that the engine is running and has completed the start sequence.

• Engine restarts in reverse from Auto Stop. This is a normal operating characteristic as the engine will restart any time the gear selector is in reverse. When reverse remains in electric mode, however, the engine restarts to provide an audible indication to pedestrians.

• Slight bump in driveline during acceleration. This is due to transition from V4 to V8 and vice versa. In Mode 2, the engine is able to operate longer in four-cylinder mode under light throttle for improved highway fuel economy. As more power is needed, the system will transition to V8 Mode. This is a normal operating characteristic of a hybrid powertrain to maximize fuel economy.

• Low pitch noise during Auto Stop. This is a normal characteristic operation of electric coolant pump or hybrid battery fan. During Auto Stop, the engine isn’t running and the interior cabin is quiet. These pumps run to keep the electronics from overheating, even in cold ambient temperatures. This noise may be more evident during high ambient interior temperatures. Advise the customer to keep the battery vents clear and not to carry cargo in the second row footwell area. The electric coolant pump runs in Auto Stop to circulate coolant to the HVAC system to maintain cabin temperature. That pump (under the right conditions) will run and may be barely audible.

• 12-volt operation. In order to maintain peak capacity in the 12-volt system, it’s recommended that customers allow the vehicle to remain in “run” when parked and attended. When the ignition switch has been turned to crank and is set to “run,” the engine will run until the desired state of charge in the 300V battery has been reached. At that point, the vehicle will enter auto-stop mode, and the Accessory Power Module (APM) will continue to power the 12-volt system. Failing to allow the APM to power the 12-volt system could cause discharge of the 12-volt battery. Examples of activities that may cause stress on the 12-volt battery include: tailgate celebrations, usage of the rear seat entertainment system with the vehicle off or listening to the radio for extended periods of time with the vehicle off. In these situations, the recommended operating mode is to start the engine. Normally, the vehicle will enter Auto Stop mode and, as the 12-volt battery needs charging, the system will automatically start the engine to keep the system fully charged. In addition to allowing the APM to power the vehicle’s 12-volt system, special care should be taken when storing this vehicle. If the vehicle is to be stored for more than 20 days, the 12-volt battery should be disconnected. If the vehicle is to be stored for more than 60 days, the 12-volt battery should be charged to capacity no less than once every 20 days.

If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service,your 5 star rating is appreciated.You can rate at any time and we can continue to work on your question as this will not close out your question.Keep in mind in some cases it can be difficult to fully diagnose or help repair your vehicle without seeing it and I work on delivering the best possible answer from what I see to work with.

Thanks Pete

Customer: replied 10 months ago.
I can add that it seems as if the car struggles more when the AC is on. When it's under a load. Could this be anything computer related? Besides the ECM as I mentioned this was replaced
Expert:  Pete replied 10 months ago.

If it struggles more with the ac on this helps pinpoint that this issue is most likely the 12 volts battery or the throttle body as both of these acting up will cause this issue and act up more with the ac on.With the ac on this draws more 12 volts from the battery and if there is a 12 volt battery fault or cable fault this will make it worse.Also with the ac on the throttle body needs to idle up slightly and if the throttle body has an internal issue this will cause this fault as well.

I would have these checked into/focused into further to locate which is the cause as I suspect one of these is an issue for this here.

Let me know if you need anything else and feel free to rate my help here as this is how I receive credit for my time.Your 5 star rating is appreciated

Thanks Pete

Customer: replied 10 months ago.
The battery was replaced last summer ... so if I check it and it's low - maybe an alternator issue? Seems like the engine light would have gone off for that but I'm just thinking out loud. And wouldn't the engine light go off if the throttle body was bad as well? Thx for the help
Expert:  Pete replied 10 months ago.

Usually the engine light would set a code for each but I have seen issues with the battery or alternator at fault on the Hybrid models and not turn on any lights so I would check into these as the cause here.Have the battery load tested and the alternator tested.

If these are o.k. it is still possible that the throttle body is the cause here as sometimes it can act up with the throttle plate operation due to carbon or a mechanical fault and the computer may see it as normal operation and not set a code.So both are still a major possibility for this issue here and most common.

Let me know if you need anything else and feel free to rate my help here as this is how I receive credit for my time.Your 5 star rating is appreciated

Thanks Pete

Customer: replied 10 months ago.
I took my car to advanced and ran test on battery and alternator. Both are perfect. If it is in fact the throttle body - doing some research online it appears my model and year could have the throttle body covered under a "special coverage adjustment". Is there a way to see if this is true by running the VIN number I gave you? Thx again
Expert:  Pete replied 10 months ago.

Yes this is right.Due to the common failure of it this may be covered under special coverage all depending on the VIN and mileage and build date.Unfortunately the only way to find out for sure if your model fits this is to contact a dealers service department and ask them to run your VIN to see if this is covered under special coverage warranty.If they do not know or if it doesnt say then they will need to check the throttle body and test it to see if they can get it covered or if this is a customer pay repair.

Let me know if you need anything else and feel free to rate my help here as this is how I receive credit for my time.Your 5 star rating is appreciated

Thanks Pete