Key details are still often left out when it comes to diagnostics
One of the beefs I have with the data we are provided by different vehicle OEMs is that they decide what goes into the service manuals and our scan tools.
Unfortunately, there is vast amounts of information and data left out that is critical for being able to properly diagnose vehicles accurately.
Should be straightforward
Case in point, we looked at a 2005 Toyota Highlander 3.3L with a check engine light on and trouble code P0018 stored. (figure 1) A quick look at the code description describes it as a CMP, CKP correlation error. This should be a straight forward diagnosis and should involve nothing more than looking at camshaft timing data on a scan tool and having bi-directional control to manipulate the valve timing.
However, when we went to look at the camshaft timing data on the scan tool the only data provides was a status message of whether the valve timing system was on or off. (figure 2) Not much to go on.
This leaves the diagnostic trouble tree as our best source of information on how to diagnose this fault. The trouble chart calls for an inspection of the timing marks on the camshaft timing gears and crankshaft. If the marks line up them we are instructed to replace the ECM. The marks were checked, they lined up properly so the next move according to the service information would be to replace the ECU. I don’t know about you but I am not really convinced that the ECU is bad but due to the lack of service information we are going to be forced to come up with another way to determine what the fault is.
All we can really get from the trouble tree is that the ECM thinks that the CMP and CKP are out of alignment.
Belt or valve timing issue
Theoretically, if the CMP CKP alignment is out then the problem has to lie with the timing belt and gear or the variable valve timing system. The question now becomes how to we determine where the failure is. We started by looking at the VVT mechanism.
We used code P0011 (camshaft timing performance) to find the test procedure for the camshaft phasers. This involved actuating the phasers with the engine running and listening for any rough running or stalling. In our case the engine stalled when each bank was activated. This would seem to indicate that the VVT mechanism was working. That left us with CMP CKP alignment. Using the methods described in the manual yielded a pass but the ECM kept flagging the code. We decided to test the valve timing using an in-cylinder pressure transducer. We measured a difference in valve timing of 20 degrees between bank 1 and bank 2. Clearly the engine timing was not correct.
This gave us the confidence to tear down the top of the engine where we found a sheared locating pin on the bank 1 camshaft phaser.
All of this could have been done much faster and more accurately if the manufacturer had provided better scan tool data and better information on the code and diagnostics procedures. This is by no means an isolated case. In my opinion when we look up codes and service information we should have everything pertinent to the system or code at our finger tips. Until this improves, diagnostics will always be a challenge.