2002 Jeep Liberty 3.7L 4x4 No Check Engine Light but Shows P0158, P0340, and P0443 Codes - How to Diagnose and Fix at Home

Important note: Not all OBD-II codes will trigger the check engine light (CEL), especially if they are pending or stored in history. The key-on-off cycle does not guarantee code display. Questions to clarify: 1) Does the CEL flash for about 2 seconds at every start? If yes, that indicates a basic signal is present — but it may not illuminate fully. 2) Are these codes current (active) or stored in history/pending status? 3) Try clearing all codes and then drive the vehicle. Recheck after driving to see if they return. Code breakdown: P0158 – O2 Sensor 2/2 Voltage Too High — indicates a possible issue with downstream oxygen sensor reading. P0443 – Evaporative Emission Purge Solenoid Circuit Fault — this is a common issue in older vehicles and may be related to wiring or vacuum leaks. P0340 – No Camshaft Reference Signal at PCM — strongly suggests a faulty camshaft position sensor or intermittent wiring connection.

I cleared all codes using the OBD11 scanner and drove about 35 miles with no issues. Upon returning, the same three codes reappeared, including a new one: P1391. I repeated the code clear process this morning, and now only P0340 remains. The vehicle still runs smoothly — full power, no shakes or stutters. Given that it's a 325,000-kilometer Canadian model with strong performance, should I replace the camshaft position sensor (CMP) with an OEM part from the dealer, or should I first inspect and test all wiring connections? I'm considering aftermarket options due to cost concerns.

P0340 and P1391 together point strongly toward a loss of signal from either the camshaft position sensor (CMP) or crankshaft position sensor (CKP). These issues typically require lab-grade diagnostic tools like an oscilloscope to properly analyze waveforms. A professional scanner with real-time data analysis is needed for accurate diagnosis. In practical terms, if the vehicle runs smoothly and shows no mechanical symptoms, start by inspecting the CMP wiring harness — especially the connector at the sensor end. Look for corrosion, loose connections, or physical damage in the first few inches of wire leading to the sensor. Many failures occur right where wires connect. My recommendation: Replace the camshaft position sensor using an aftermarket unit. The cost of labor versus cleaning and reinstallation is often better than a full repair. Given 325,000 km, this may be a more cost-effective long-term fix.

I plan to replace the camshaft position sensor with an aftermarket unit from CarQuest in Montreal. Before doing so, I will thoroughly inspect all wiring and connectors related to the P0340 code. Given my age (78) and the cold weather conditions here, I want to ensure any repair is safe and reliable. Thanks for the prompt advice — it’s greatly appreciated. I’ll update once I’ve completed the inspection and testing.

Good morning from Montreal, Quebec! After reviewing all my codes (P1391, P0158, P0340, P0443), I discovered that the P0443 issue was caused by a corroded evap purge solenoid connector. I unplugged it, cleaned the contacts, and reconnected it. I also inspected all fuses in the fuse box near the battery — many had green corrosion due to poor maintenance over time. After cleaning every connection, I performed multiple key-on-off cycles with no codes appearing on the scanner. The vehicle has been driven hard on highways today with full performance and zero issues. I saved hundreds of dollars by fixing it myself. Thank you all for your help — this old man finally knows how to maintain his Jeep properly!

Dieu sauve la reine

I drove approximately 200 kilometers yesterday afternoon and checked the scanner every 20 minutes. No codes have appeared — not even P0340. I believe the root cause was long-term neglect of electrical connections, including fuses and wiring. Thanks to your suggestions and some basic maintenance (elbow grease), I’ve cleared all issues at home. I’ll keep the scanner connected for the next few weeks as a precaution to monitor if any codes reappear. Thank you again — this has been a valuable learning experience.

Hi again — today, P0340 (Pending) reappeared after checking wiring and fuses. I performed a full reset and still see it. However, the vehicle runs perfectly with no performance issues. Does 'pending' mean that the sensor is failing or that it needs replacement? I’m trying to understand whether this code indicates an imminent failure or just a temporary signal issue.

Suddenly, when I close the tailgate, interior lights stay on, dashboard glass indicator flashes continuously, and the rear wiper stops working. The actuator operates normally — all doors open/close properly with the fob. Could this be due to a microswitch in the tailgate handle? Or is there a faulty switch inside the actuator giving false signals? This issue started after my battery died 24 hours ago, which suggests an electrical fault triggered by power loss.

Road salt exposure can severely corrode tailgate components. Remove the inner panel and clean all mechanical parts with penetrating oil and electrical contacts with contact cleaner or Brake Kleen. This often resolves both lighting and wiper issues caused by corrosion.

I tried Mohawkmtrs' suggestion — no improvement. The Jeep runs perfectly, with full power and all functions working except the interior lights that stay on and the dashboard glass indicator flashing continuously. I can stop it by pressing the trip button. The tailgate actuator works fine (opens/closes/locks), but the rear wiper does not operate. All these issues began at once. I cannot afford a garage visit — an hour-long service would cost nearly $100, which is unaffordable. If anyone has insight into what could be causing this, please share. Thank you, oldjohn1940.

BBBind.com provides a detailed schematic of interior lighting and control systems. Without actual voltage/ohm testing with a multimeter, it's difficult to pinpoint the exact cause. The flashing 'glass' indicator in the dash — if it only stops when pressing the trip button — may indicate a faulty switch or short circuit in the tailgate module or actuator wiring.