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1996 Lexus ES300 P0340 Fault: Camshaft Position Sensor Issue & Troubleshooting Guide

Model: Lexus ES300 Fault Code: P0340 Posted: 2009-10-21 10:04

I'm experiencing a recurring P0340 fault on my 1996 Lexus ES300 V6, and I'm seeking reliable troubleshooting steps to resolve it. The issue began with a noticeable misfire in cylinder #4, which was traced to a valve shim that had shifted out of alignment. After correcting the valve shims and reassembling the engine, the car initially ran smoothly. However, after another oil change and rechecking the valves, the engine warning light activated immediately upon starting. The vehicle now exhibits severe idle instability and transmission shifting problems—when accelerating, it runs up to redline before shifting, requiring frequent throttle release to allow gear changes. An OBD2 scan confirms a single P0340 code: 'Camshaft Position Sensor Circuit Failure'. I replaced the camshaft position sensor with a new unit (WELLS PN SU4042), but the issue persists. I've verified wire continuity from the sensor to the PCM, and there are no shorts or opens. I also tested the wiring with spliced replacement wires—no improvement. Given that I don't have access to a PCM for testing, I'm wondering what other diagnostics should be prioritized before considering more complex repairs. I only recently touched the camshaft sensor during an oil filter change, and my arm merely brushed against it—so I suspect no physical damage occurred at that time. I’m looking for clear, step-by-step guidance on diagnosing P0340 in a 1996 Lexus ES300 V6. Are there known issues with valve adjustments affecting cam sensor readings? Could a damaged reluctor ring or timing misalignment be the root cause? Any insights from experienced mechanics or owners of this model would be greatly appreciated.

Related fault codes
P0340
Comments (6)
Anonymous 2009-10-21 15:01

A misaligned valve adjustment or improper timing belt alignment could also trigger a P0340 code. Additionally, damage to the crankshaft position sensor reluctor ring might interfere with camshaft signal detection—these are common causes in older Lexus ES300 models.

Anonymous 2009-10-21 18:53

I've just completed all the checks and confirmed that wiring is intact—no ground faults or open circuits. The sensor harness appears undamaged, and I’ve verified continuity throughout the circuit.

Anonymous 2009-10-21 22:12

Even with a new sensor, it's important to verify whether the wires are conducting current properly. Does the camshaft position sensor have an adjustable air gap? How do you know the replacement sensor is functioning correctly?

Anonymous 2009-10-21 23:50

I wish I had an oscilloscope available to measure the sensor output directly—this would provide definitive proof of signal integrity. However, even with a brand-new sensor, it's possible that the unit isn't properly calibrated or is defective. Most 1996 Lexus ES300 models don’t have adjustable air gaps for the camshaft sensor.

Anonymous 2009-10-22 05:18

A 'new' sensor doesn't always guarantee functionality—many aftermarket units fail to perform correctly out of the box. An oscilloscope would be ideal, but it's possible to diagnose without one. What brand and model number do you have for your camshaft sensor? Is there any visible damage to the reluctor ring or timing components?

Anonymous 2009-10-22 07:13

Sensor Brand: WELLS, Model Number: SU4042. The physical unit appears intact, and I've carefully inspected the reluctor ring—no signs of wear or damage.