Catalytic converters must be warm before they can work properly. On a cold start the PCM provides a rich mixture to keep the cold engine running.
All that extra fuel goes into the catalytic converter. But the exhaust isn't very hot, because, ah, the engine is pretty cold. GM has employed several strategies to fire up the catalytic converter quicker and reduce cold start emissions. One way is to use a secondary air pump that pumps outside air directly into the catalytic converter.
As the engine heats up and combustion becomes easier and more complete, the PCM will command the idling control valve to increase the amount of air entering the engine to suit the changing conditions. However, when the load on the engine changes, say, when some electrical consumers or other systems are either turned on or off, the PCM adapts the signal voltage to the idle control valve to ensure that the idling speed remains stable, and at the RPM specified by the manufacturer.
For battery power supply ecu circuit open check engine light is perhaps the most troubling of lights because it could mean so many different things, from you didn't screw the gas cap on tightly enough to look out for pistons flying through the hood and into the stratosphere. The easiest way to find out what this light is telling you is to hook your vehicle up to a scan tool. P2991 error code diagnostic tool looks a little like an oversized calculator and plugs into a communication port inside the car. After you instruct it to perform the scan, it speaks battery power supply ecu circuit open with your car's computers to find out exactly what's prompting the light to turn on.
Difficulty Level (Soso)
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Repair Time (30 Min.)
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| Cost Prediction : $ 25-45 |
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P2991 is a kind of Powertrain Trouble Code
Powertrain of a modern automobile, comprising engine (with exhaust system), transmission, drive shaft, suspension and the wheels. In a motor vehicle, the term powertrain or powerplant describes the main components that generate power and deliver it to the road surface, water, or air. |
You can view according P2991 DTC for your car model. We selected several models to see obd2 solutions click and view it.
Engine OBD 2 Codes website is a freeware resource center for engine trouble codes.
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