P0161 O2 Sensor Code

[msaluta]

Have a 1997 C1500 2wd. Recently the P0161 code popped up.

I looked at the ENG-1 fuse and it's gtg.

I replaced the passenger side, downstream O2 sensor with a Bosch, inspected the wiring harness which appeared to be gtg, and cleared the code.

This resolved the issue for approximately three days. This morning the same P0161 code pops up.

I'm trying to understand what to troubleshoot next. Continuity seems obvious to test. But from there I've read some folks look at EGR valves and cats and I'm trying to replace only items that need it.

 

[df2x4]

This may seem like a strange question, but do you have an aftermarket remote start system installed on this truck? If so, clear the codes and stop using the remote start. See if the issue goes away if you start with the key 100% of the time.

 

[msaluta]

This may seem like a strange question, but do you have an aftermarket remote start system installed on this truck? If so, clear the codes and stop using the remote start. See if the issue goes away if you start with the key 100% of the time.

No remote start.

 

[Schurkey]

1997 C1500

WHAT ENGINE?

Recently the P0161 code popped up.

I looked at the ENG-1 fuse and it's gtg.

I replaced the passenger side, downstream O2 sensor with a Bosch, inspected the wiring harness which appeared to be gtg, and cleared the code.

This resolved the issue for approximately three days. This morning the same P0161 code pops up.

I'm trying to understand what to troubleshoot next.

The Usual Three:

1. Verify fuel pressure at prime, at idle, and under load. Most fuel pressure gauge assemblies have a push-button pressure release connected to crappy vinyl tubing. Route the tubing so it empties into a drain pan, then push the button while the engine is running. This simulates higher fuel demand if you can't check fuel pressure on the highway. Fuel pressure should remain steady even with fuel flowing down the pressure-relief tubing. How old is the fuel filter? Have you ever dumped a bottle of Chevron Techron Complete Fuel System Cleaner into the gas tank? (Recommended at every oil change.)
   

1. How old are the usual “tune-up” parts and procedures? Inspect/replace distributor cap, rotor, plug wires, spark plugs. Make sure the ignition coil will reliably fire a spark-tester calibrated for HEI when the coil is fully warm, and misted with water from a squirt-bottle. Cranking compression test of all cylinders while the spark plugs are removed. Verify EGR, PCV, EVAP, and Heated Air Intake (if used) systems for proper operation. Verify proper initial timing (TBI) and electronic spark advance (TBI and Vortec). Replace old O2 sensors unless you can PROVE that they're working properly—old O2 sensors get lazy, they don't provide accurate data, but they do provide “data” that fools people into thinking they're “working”.

1. Connect a scan tool (NOT a crappy “code reader”) and look for “codes”. More important, look at the data stream to verify EVERY sensor and computer output. Verify fuel trims during the time that the vehicle is not running properly. Look for misfire counts for each cylinder (OBD2 only.) “Codes” have official diagnostic procedures that will be found in the service manual set for your vehicle. The service manual set can be downloaded from the links in the Sticky thread section of the Engine forum on this web site.

 

[Supercharged111]

I'd do what you alluded to: check your power and ground back at the plug. Wiggle harnesses around if you have to.