2003 GMC Sonoma Could this be a computer issue?

Tiny
LOKI0134
  • MEMBER
  • 2003 GMC SONOMA
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 85,000 MILES
My service engine light is on, and has several codes. The brake light flashes intermittently, and once in a great while, all of the lights come on, the tach and odometer drop to 0, and then all goes back to normal. The gas gauge shows I have gas, but the truck will start spitting, sputtering, and popping, and losing power, like it's out of gas, but continues to run/start. I put gas in, and it's fine. I know I have more than one problem here, but I don't even know where to start.
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Friday, November 6th, 2009 AT 2:45 AM

3 Replies

Tiny
SERVICE WRITER
  • EXPERT
Lets start with the code numbers.

What brake light is flashing? One in the cluster? Red one orange one?
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Friday, November 6th, 2009 AT 4:58 AM
Tiny
LOKI0134
  • MEMBER
Codes are: P0120; P0420; P0101

The emergency brake light, on the instrument panel, that is red, is randomly on, or blinking, but very rarely is it off.
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Friday, November 6th, 2009 AT 6:25 AM
Tiny
SERVICE WRITER
  • EXPERT
Not sure how much I can stay with this this morning, but.

The po420 is catalyst effiency code. It does not necessarily mean the you need a converter. For example an exhaust leak in front of the converter can cause this code. Typically the CEL would be flashing when this code comes up or just before it.

PO101 has to do with air mismeasurement going into the intake. Look for a vacuum leak between the MAF and the throttle bore first. Clean the MAF with electrical cleaner.

I have no info on PO120 for this truck, but it is a throttle position code on the c series pickups.

Remove the air snorkel to the throttle, Tip in the throttle plate, any sign of carbon and I would suggest doing an intake cleaning and throttle bore service.

My thoughts are that there is a vacuum leak causing 2 codes and a build up of carbon in the throttle bore.

Check the brake booster vacuum line as well. Listen for any hissing to help you locate it and use a can of carb cleaner to spray it short bursts on suspected leaks. The vacuum leak will suck in the carb cleaner and change the idle temporarily.
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Friday, November 6th, 2009 AT 7:17 AM

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