1998 Chevrolet Z71 P0300 P0151 P0174 - Fuel Pressure & Oxygen Sensor Diagnostics

60 psi is unusually high for a 1998 Z71—especially in colder weather. There's a known fuel filter located on the driver-side frame rail that may have degraded over time; I recommend checking and replacing it, as this filter was removed in later model years but was present in early '98 models.

I replaced the driver-side fuel filter when installing a new fuel pump. I'll contact the dealer where I purchased the pump and filter to confirm the manufacturer's recommended fuel pressure specifications for this model year and configuration.

Morning Kevin—P0157 indicates low voltage on bank 2, sensor 2 (b2s2). The signal reads 0V. Is this a wiring/connection issue or could it be due to another cause? I recently replaced both downstream O2 sensors on the right side; fuel performance improved temporarily before P0157 appeared. The b2s2 sensor is located above the transmission, which makes access difficult—perhaps I missed the 'click' when connecting. I did a smoke test and only saw emissions from the resonator to throttle body area, possibly due to a 3-inch o-ring leak. No noticeable leaks were detected during operation or movement. Thanks for your input.

Most likely cause: wiring issue. The PCM sets P0157 when the vehicle runs out of fuel or experiences a sensor signal failure. Key troubleshooting steps: - Check HO2S wire connections—sensor pigtail may be touching exhaust manifold or system components, which disrupts oxygen supply. - Inspect all HO2S wires and connectors for breaks, contamination, or corrosion. - Test for intermittent ground in the signal wire between connector and sensor. Other potential causes: - Lean injector condition: Perform Injector Balance Test to check fuel delivery balance. - Fuel contamination: Water near the in-tank fuel pump inlet can reach injectors, causing lean exhaust and triggering P0157. Refer to Alcohol/Contaminants-in-Fuel Diagnosis. - Low fuel pressure: A system that runs lean will trigger this code. See Fuel System Diagnosis. - Exhaust leaks: Leaks near the HO2S sensor cause a lean condition. - Vacuum or crankcase leaks: These can also lead to a lean mixture. If all these checks are normal, the issue may lie with the oxygen sensor itself.

Dadgum teacher... I'm gonna have to sharpen my pencil. Thanks for the insight though!

I haven't resolved P0157 yet, but I recently removed and inspected the distributor. The gear was worn—this may have contributed to misfires. I installed a new distributor from NAPA. The original had stripped threads in the cap screw hole and a broken tab, requiring me to use washers and nuts to secure it (a real pain). I also learned that some distributors come with copper leads instead of aluminum; I previously used an OEM unit with aluminum leads. The new NAPA distributor has a metal body, includes a crankshaft position sensor, cap, and button. Its cap features copper leads—verified by inspection. I just installed it about an hour ago. The cam timing was set correctly at zero degrees. Previously, the original distributor was misaligned (I estimate it was off one tooth), which may have caused a -13° retard reading. After reinstallation and road testing, idle is stable with no immediate misfires. I also fixed an exhaust leak on bank 2—this likely helped reduce the P0300 symptoms. While P0157 remains, the truck is now running much better. Thanks again, Kevin. I’ll send photos separately when possible.

I swapped out my downstream O2 sensors on bank 2 and cleared the code. So far, no return of P0157—will monitor over time for recurrence.

It's been about three months since I last saw the SES light. MPG isn't a major concern on this truck—I usually carry 150–200 lbs of payload. The truck has held up well under regular use. I don’t remember that being one of its selling points. I’m confident it’s stable for now—knock on wood. If there's a problem lurking in the yard, I’ll be the first to notice. Thanks again, Kevin.