One of our longtime customers brought in her 2011 Lexus LS460 (4.6-liter V8). She stated that it was time for service and the check engine light was on. She also said that the car had been running well.
Once we got the car into the shop, we connected the scanner and pulled codes. We pulled P0015 camshaft position (CMP) B timing over retarded (Bank 1), P0365 camshaft position (CMP) sensor B Circuit (Bank 1), P0368 camshaft position (CMP) sensor B Circuit input high (Bank 1) and P1604 startability fault.
A quick refresher on a variable valve timing system (VVT). Once computers took over engine control, there was no longer a need for certain mechanical parts (such as ignition distributors). The computers are able to calculate top dead center (TDC) from information from the cam and crank position sensors. Cam and crank position sensors tell the engine computer where the piston and valves are. Once the piston reaches TDC on the compression stroke, the air and fuel have to be ignited. The VVT system directs high-pressure engine oil to the adjustable cam gears. Once enough oil pressure is applied, the cam gears can adjust (phase) as much as 30 degrees. For example, if the car is in a heavy acceleration, the timing should advance and during a deceleration it will retard. Either way, it is making sure the cylinder detonation is as efficient as possible.
This particular V8 has one cam sensor, one crank sensor and four VVT sensors. Bank 1 is on the driver side and has cylinders #1-4. Bank 2 is on the passenger side and has cylinders #5-8. The cam sensor is on the passenger side of the engine and is taking a reading from the timing chain. The crank position sensor is on the bottom of the engine and is taking a reading from the crank gear. The four VVT sensors are reading the Bank 1 and Bank 2 exhaust and intake camshaft positions.
The first thing we did was check the engine oil level. We need to do this because the whole VVT system is driven by oil pressure. If the engine oil is low, the VVT cannot operate normally. The oil level was good. We then checked the connectors to the cam sensor and the Bank 1 VVT sensors (all were OK). Then we swapped the Bank 1 exhaust and intake VVT sensors, cleared codes and test-drove. The same codes came back. We then disconnected the Bank 1 sensors (exhaust/intake) and back-probed to the engine control module (ECM). We found that the Bank 1 intake sensor harness was OK, but the Bank 1 exhaust sensor harness had an intermittent signal. We then performed a wiggle test and could turn the sensors off or on by just touching the wire in the middle of the harness. We then cut back the insulation and found three compromised wires.
This particular engine wire harness is extremely expensive, so we repaired all three wires and put the car back together. Once together, we cleared the codes and test-drove the car. The problem was gone.
A good lesson here for the do-it-yourself mechanic is that codes will only point you in the direction of the problem. Usually we have people show up and say they had already replaced the cam sensor, yet it did not solve the problem. You always have to complete the test plan to get to the root of the issue. This engine was running fine because the cam sensor and the crank sensor were not compromised. It was the Bank 1 exhaust sensor wire harness that had the problem. The VVT sensors just tell the computer that the VVT system is working correctly, but don’t actually give the adjustment command. Remember to test, test, test. Thanks for reading.
Matt Pataky owns Sunnyvale Foreign Car Service, 15 Pioneer Way, Mountain View. For more information, see sunnyvaleforeigncar.com.
