2003 GMC Truck OBD II CODES

JEFFERYALLISON

MEMBER
2003 GMC TRUCK

Computer problem
2003 GMC Truck V8 Four Wheel Drive Automatic

My truck is running very rough and sounds like it is backfireing thru the intake. It is also now showing codes p0138 & p0158. Could two sensors have gone out at the same time? Or is something else more likely?

3 Replies

RASMATAZ

MECHANIC
75,992 POSTS

Those codes applies to oxygen sensors could be it causing your problem if there not switching

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Wednesday, April 29th, 2009 AT 9:56 PM

JEFFERYALLISON

MEMBER
3 POSTS

Rasmataz, thanks for the response!

I should have noted in my question that I am aware that both of the codes refer to the o2 sensors that are after the cats. What I don't understand is if it makes sense that both o2 sensors would quite at the same time or if there is a more likely suspect that could cause the same DTC's? I have just purchased a pc based scaning program and plan to use it to help me test the voltages, but I really don't think I have a good understanding of how all the electronics work together. Any additional help would be greatly appreciated.

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Thursday, April 30th, 2009 AT 5:16 PM

RASMATAZ

MECHANIC
75,992 POSTS

A low voltage (lean) reading may indicate a bad O2 sensor, a vacuum leak, or a condition that allows unburned oxygen to enter the exhaust. Check intake vacuum at idle, and inspect vacuum hose connections. If okay, check for a misfiring cylinder, a burned exhaust valve that is leaking compression, or a leaky exhaust manifold gasket.

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Thursday, April 30th, 2009 AT 5:56 PM