1999 Honda Civic EX Check Engine Light On: PO141 & PO135 Codes Explained
My daughter drives a 1999 Honda Civic EX, and the check engine light has been on for about one month. Approximately one month ago, I replaced both the upper and lower oxygen sensors, but the light still remains illuminated. Recently, the car has stalled twice while idling. Using an Actron OBDII scanner, I retrieved fault codes PO141 and PO135. I'm not familiar with these codes or what they indicate, and I'm unsure of the next steps to resolve this issue. As a diesel mechanic with experience in older vehicles, I typically don't work on imported cars like this one. Any guidance would be greatly appreciated.
Hi Bill, Codes PO141 and PO135 indicate a circuit fault with both oxygen sensors. It's relatively rare for both sensors to fail simultaneously. First, check the HO2S connector for any short to ground or abnormal voltage readings. Also inspect for wiring breaks between the sensors and the ECM/PCM. If no issues are found in the wiring, the problem may point to a faulty ECM, which would require replacement.