99 7.4 O2 Sensor Problems P0134

tryingtolearn · November 22, 2009

I have a 99 GMC C3500 with a 7.4. It ran bad for a while (a few months) before the SES light came on. Scanned it and got a P0171. Changed out the B1S1 o2 sensor with a aftermarket Bosch and fresh plugs. Engine continues to run horrible but the new DTC is P0134 (B1S1 Circuit no activity). For the life of me I can't track down the problem other than going with the factory O2 sensor but at $177.00 I need to make sure that is the problem. Anyone have any suggestions. I read earlier that someone had the same symptoms but not the same DTC. They changed out the Fuel Pump Relay. Doubt it'll make a difference but it is worth the try. The only other known problem is the fuel gauge went out a month or so ago. Going to also try a new fuel filter, it's time anyway.

Will try to upload freeze frame tomorrow.

96chevy7.4L · November 22, 2009

Hi there. My 7.4L is the one that ran like crap. NEVER blinked a code which is why the guess began. I ended up putting the fuel pump relay in it and got lucky and that fixed the prob. The relay was getting hot I later found out and that was causing the issue. The bosch O2 sensors usually are pretty good. You might disconnect the battery for 20 minutes or so and let the computer reset after the O2 sesnor. How long has it been since you put a cap and rotor in your truck. The 7.4L's are notorious for eating up rotors. That will make it run bad also. If it ever puff's white out the tail pipe and then doesn't start that is a rotor also just for future reference. A fuel filter change would be a good idea. But be warned putting a cap and rotor in is a PITA. Hope this helps. Feel free to ask any questions. I have had 2 od these 7.4L's now so I am pretty good with them.

tryingtolearn · November 22, 2009

Thanks for the advice i will try changing out the relay and disconnecting the battery. Changed the cap and rotor about 6 months ago when the issues first started.