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Tackle other-worldy vehicle problems by relying on the data

Saturday, October 1, 2016 - 07:00
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With Halloween coming up, I have lately been reminded of the short-story horror series, Tales from the Crypt. That’s because every so often some of the vehicle problems we encounter can seem sort of paranormal. Even though we keep telling ourselves that there must be some logical explanation to what is causing the fault, the data we are observing is incomprehensible and our usual tried-and-true testing reveals little or no guidance. With that theme in mind, here’s our first story.

2007 Toyota Camry with Code P0606 ECM Processor Error

On this vehicle, I needed to program a new ECM that had been diagnosed and installed by another tech. Maybe programming isn’t the proper term, however, since pretty much all that was needed was a VIN Write, but I was happy to oblige. When the tech got back from the test drive, code P0606 was already set, and I was asked to go over the diagnosis that led to the ECM needing to be replaced. Now, even though there needs to be some verification of the controller’s power(s) and ground(s), when you get an internal processor code it is highly likely that you will be replacing the ECM, so what went wrong on this diagnosis? 

After a short test drive with a new PCM installed, the same Code P0606 returned. This is the only code that is set which is why the technician ignored the code flowchart that had the O2 sensor codes combined with the P0606. They instead followed the code flowchart for P0606 Only, which simply states to Replace ECM.

When looking at the trouble code flowchart, I noticed that there were two options for diagnosis; one for a P0606 stored with other codes and one for a P0606 stored by itself. Well, only the P0606 is stored with nothing else even in pending status, so according to the flow chart: REPLACE ECM. No testing, no checking, nothing, just replace. Ok, I can see where the tech called for the replacement ECM, and he was justified in making the call. But there had to be a reason the same code would reset with a new OEM ECM. My first thought was a poor ground connection, so I used an ECM connector pin out from ALLDATA and my LOADPro dynamic test leads to check the integrity of the grounds for the ECM. If you’re not familiar with the LOADPro, it is a device that replaces your regular voltmeter leads and allows you to perform a dynamic voltage drop test with a push of a button on the circuit you are testing. Well guess what? Grounds test fine with virtually no voltage drop. Since I’m here, let’s check the voltage supply, too. Same thing. The terminals of the harness connector also passed a pin drag test.

At this point, I am getting the eerie feeling that we received a defective ECM, but what are the odds that a new ECM would have the exact same problem as the one we replaced? Maybe this vehicle is possessed. Remember when I looked up the code and there were two options listed for P0606? A lot of times, if there are multiple codes, it would make sense to ignore a certain code if other codes are set that have a higher priority, or it could be that they could cause that code to set. Well the other codes are oxygen sensor codes. Could an O2 sensor cause an ECM processor malfunction? Yes, according to the code set criteria. A malfunction of the Air/Fuel Ratio Sensor transistor or the Heated Oxygen Sensor transistor could cause the ECM to believe there is an internal processing error. After hooking up the scan tool and graphing the data from the oxygen sensors, I couldn’t believe what I was seeing. Looking at the impedance or the Rear Oxygen Sensors, it was easy to see that while Bank 1 Sensor 2 was reading in the range of 90 ohms, Bank 2 Sensor 2 was exhibiting spikes up to 21,247ohms! I guess that is something that can trick an ECM. 

Something I have not monitored before but definitely looks out of place is the impedance for the B2S2 Oxygen Sensor. Note that is as several spikes reaching over 21,000 ohms, ultimately this is what was setting the ECM processing error.
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