Questions and Answers

Chevy CK 3500 DTCs P0172 And P0175 Q. Over the past few months I have been receiving the following two DTC codes P0172 and P0175. They seem to alternate between each other in that I will get P0175 clear it and within the week I get P0172. I clear it and once again within a week I get P0175 again. I have had the fuel regulator, dealer replaced this item, the Mass Air Flow sensor, dealer replaced this item, and two catalytic converters replaced, they went bad.

My engine has the following performance items added: Helix throttle body spacer, Airmax air intake filter system and true dual exhaust. I also have a ProFlash engine programmer that I use to set the truck up for towing or economy mode, checking DTC codes etc. However, I have been receiving the above two codes for a long time before the performance items were added to the engine. I am not sure what to look at next. Do you have any suggestions?

• 1999 Chevy CK 3500 Crew Cab Dually
• 7.4 liter 454 Vortec
• Automatic Transmission
• 84,000 miles
• Fuel Injection
• ABS brakes
• P/S, A/C, Cruise control

Jeff
Merritt Island, FL

A. If I'm not mistaken, these codes are both rich mixture codes. That leads to high fuel pressure, a misfiring cylinder, oxygen getting to O2 sensors, lot's of possible problems. A scanner hooked up on a test drive will tell you what the O2 sensors are doing and may give you a clue as to what's going on.

Hint, if you have a leak in an exhaust manifold, it will leak out exhaust and also pull oxygen into the exhaust stream. This oxygen will pass by the O2 sensors and truck will THINK it's running lean. So the PCM will fatten up the mixture for this false lean signal. Very tricky situation here. You may need some expert help to find this problem.