Locking in on a sensor problem affecting a 2005 Toyota RAV4

Jun 30, 2023

A new customer brought in her 2005 Toyota RAV4 L with a 2.4-liter engine last month because the vehicle had an extremely bad engine oil leak.

She said the leak began after another shop performed an oil change. After checking the car, we found oil pouring out of the valve-cover gasket. There was so much oil on the engine that we advised her to get the engine professionally cleaned before we worked on the car.

The engine bay was extremely clean when the RAV4 returned to our shop, and we replaced the valve-cover gasket. We also installed new spark plugs – because the customer wasn't sure when they were last replaced – and a positive crankcase valve, as it sits in the valve cover. After we test-drove the car, the customer took it home.

Three weeks later, she stopped in to tell us the car would intermittently stall when coming to a stop.

We checked the car but could not confirm the problem. The check-engine light wasn't on, but we did pull one diagnostic code from the car's computer: P0420 (catalytic converter efficiency). This code did not really pertain to her complaint, but it led us to check the throttle body.

When the customer brought the car back for repair a week later (she didn't have time that day), we pulled codes P0353 (ignition coil primary/secondary cylinder No. 3), P0341 (camshaft position sensor) and P0420 (catalytic converter efficiency below threshold). The catalytic converter code was the same, but now we had a cam sensor code and a coil code.

Because Toyotas are notorious for having stuck idle control valves and dirty throttle bodies, we performed the throttle work first. The idle control valve sits on the throttle body. If the idle control is stuck, the engine will just die as it decelerates. The only way to fix the problem is to clean or replace the automatic idle control valve.

The customer gave us the authorization to take the throttle off and clean the throttle and idle valve. What we found next was unusual. Upon removing the throttle, we discovered a hardened piece of silicon stuck in the throttle's inlet cooling port. When I first saw it, I was taken aback – I have never seen anything like that before. I also knew it probably didn't cause the customer's problem. Sure enough: After we cleaned, installed and adapted the throttle, the problem remained.

We then checked the camshaft position sensor and its connector and made sure we could see the live data coming from the sensor. Cam sensors can be tricky because they will drop out intermittently; if you test one while it's working, you may never find the problem. There was a little residual oil in the connector, and we cleaned that out. We then swapped the No. 3 coil for the No. 1 coil to determine whether the problem was with the coil, plug or something else. We then cleared the codes and drove the car.

During the test-drive, it stalled at a stoplight. When we turned the car back on, codes P0353 and P0341 reappeared. The coil code stayed in the No. 3 cylinder and did not go to the No. 1 cylinder, so we figured the problem could be in the primary ignition.

We then cleared the codes and drove the car with the scanner connected, with someone in the passenger seat checking live data on the scanner. He watched three important sensors: crank sensor, cam sensor and engine coolant temperature sensor. When the car failed again, we noticed that the crankshaft sensor dropped out.

We drove the car back to the shop and checked the crank sensor. With the car running, our technician put his hand on the crankshaft sensor wire and wiggled it. The car died immediately. He then pulled on the connector and it came right off – the crankshaft sensor connector was not locked in. He locked it and the car didn't die again.

Interestingly, the crankshaft sensor circuit never created a code. Even more interesting: The No. 3 cylinder coil – not 1, 2 or 4 – created a code.

After further research, we figured out the crankshaft sensor connector was on just enough to let the car run but did not create a code. Also, the main engine computer was getting only a partial signal from the crankshaft sensor and got confused and thought the problem may have been coming from the cam sensor or the No. 3 coil. We think what happened was that because the crankshaft sensor connector was not locked, it got moved during the engine clean.

I called the customer a few days after the repair and she said the car had more power than it had for a long time. I told her the extra power she felt was because the throttle plate was now clean and the mystery peace of silicon was no longer blocking coolant flow to the throttle body. Because the throttle body knew the correct temp, it could now operate normally.

Matt Pataky owns Sunnyvale Foreign Car Service, 15 Pioneer Way, Mountain View. For more information, call 960-6988, email [email protected] or visit sunnyvaleforeigncar.com.

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