You can't fix it the old way

Aug. 5, 2015
As you are working on today’s vehicles you won’t be able to fix many different vehicle problems unless you are able to reprogram the vehicle. Our case in point is a 2006 Ford Explorer with a 4.6L V8 (Figure 1) that came in the shop with an EVAP circuit and O2 heater circuit problem. 

As you are working on today’s vehicles you won’t be able to fix many different vehicle problems unless you are able to reprogram the vehicle. Our case in point is a 2006 Ford Explorer with a 4.6L V8 (Figure 1) that came in the shop with an EVAP circuit and O2 heater circuit problem. The associated DTCs were P0141 (O2 heater Circuit Bank 1 Sensor 2), P0161 (O2 heater Circuit Bank 2 Sensor 2) and P0443 (EVAP System Purge Control Valve Circuit). Other than these DTCs, the vehicle ran fine but with the MIL illuminated the vehicle would not pass inspection.

The first place to go after the customer interview and a visual inspection is the service information. We decided to start our search with Identifix since they do a good job covering old problems and provide OE information. We found the same Diagnostic Trouble Code (DTC) information listed on Identifix suggesting a wiring issue or a defective PCM could cause the concerns. We decided to start our formal diagnosis by checking the P0443 EVAP circuit first since it would be easier. The DTC description stated that this DTC can set if the EVAP canister purge valve circuit output driver is out of range. The PCM test fails when the solenoid is outside of the minimum or maximum limits that are set for the commanded state. The possible causes for this code are VPWR (vehicle power circuit) circuit open, EVAP canister purge valve circuit shorted to ground, damaged EVAP canister purge valve, EVAP canister purge valve circuit open, EVAP canister purge valve circuit shorted to VPWR or a damaged PCM.

With all of those possibilities it is easier to check at the load first to see if there is power and ground along with checking if the solenoid works. Since the canister purge valve would be easy to test right at the load we started there. We disconnected the wiring to the purge valve with the ignition key off and turned it back on to check the indexing of the two-wire connector to make sure which one of the two had power. Using the index information, we used a PowerProbe to manipulate the solenoid. The PowerProbe tip was connected to the B+ side of the solenoid and the ground wire to the other side along with a mini amp clamp that was placed around the ground wire. Now we could check the load, the EVAP solenoid to see if it works and how much amperage the solenoid would draw. This test was one easy complete way to diagnosis that circuit without following a long task.

Figure 1 

In the past I have seen many solenoids drawing excessive current that would burn the circuit open. The testing we performed confirmed that the solenoid did function as designed and did not cause a high current draw that would damage the PCM.  The test concluded that the purge solenoid was drawing about 430 milliamps assuring that the valve had the ability to function properly. With the purge valve out of the way we now could move on to testing the O2 heaters. This part of the diagnosis was going to be a bear to check since this 4.6L V8 hardly had any room to get to the connectors, so we decided to test where it was easiest, at the PCM. Service information suggested checking power at fuse 42 or at the circuit breaker. Since this vehicle had a fuse and not a circuit breaker we checked it for power before moving on to a more difficult test. Since the fuse was good we had to check the PCM which was located on the right side of the passenger engine compartment making it easy to test for voltage and current draw. Now that all the easy tests were done we had to move on to test the O2 sensor heaters at the source. We struggled to get the connectors apart due to the tight space but once we did, we installed jumper wires to the heater power and ground circuits. We once again used the Power Probe and connected the tip to the B+ side and the ground wire to the ground side of the circuit along with an amp clamp attached. We proceeded to check for heater current as we depressed the power button on the Power Probe. There was normal current draw Bank 1 sensor 1 heater circuit. We moved on to the Bank 2 sensor 2 and found that also was drawing the correct current. With test results indicating that all the circuit components were good it was now time to condemn the PCM.

Remember before replacing the PCM, the most expensive fuse on the vehicle, always check for excessive current draw from components that will damage a computer. Since all the solenoids on the affected circuits did not test for excessive current it left only the PCM. We called around to aftermarket part stores trying to locate the PCM that was not available. We then called the two different Ford dealers that told us they did not have it but they can special order. The price of a new PCM was over $800.00 making the repair more difficult for the vehicle owner to swallow. The vehicle as I stated earlier ran well, the only problem was that the MIL was illuminated and it would not pass an inspection. The owner asked if there was a possibility in getting a junk yard PCM that can just be plugged in and fix the problem. I explained to them that it may be possible in locating a used unit but that the engine would not start without reprogramming the PCM. This is also true if the unit was purchased from Ford, nothing works without programming it. I also explained that I would need all the vehicle keys and key fobs so I could program them in to the PCM. After calling salvage yards for over an hour I came up empty handed.

Then I remembered the company I told you about in last month’s column, AutoECMs.com. The company will ship you a unit to try and if it doesn’t work or you don’t want it, you can return the unit for the fee and shipping. Since I was confident that the PCM was defective I purchased the unit and installed it. With the used unit installed I know the vehicle would not start without reprogramming it. I had connected my IDS to program the unit but as luck would have it my laptop that the Ford IDS was on was having a Microsoft problem. I did not want to take the chance in destroying the PCM so I decided to program the unit using my Drew Tech J2534 device that’s on a different laptop. As you can see the software (Figure 2) looks just like the IDS and works similar with the exception I had access the file and pay for it. I proceeded with the first programming screen that provided the vehicle specification that needed to be confirmed. The second screen had the mileage and the VIN information that needed to be corrected since this was a used PCM and did not match the vehicle’s VIN. The following screen had a dropdown menu that allowed me to select Programmable Module Installation that open up into another drop down menu allow me to select the PCM module that needed to be programmed. I selected the PCM and followed the screen prompts that instructed me to turn the key on and off until I reached the screen that requested the VIN information. Once on the VIN screen I typed in the correct VIN. That moved me into the PATS (Passive Anti-Theft System) screen. Now I needed at least two Ford ignition keys along with any key fobs. I selected the (Figure 3) Parameter Reset that walked me through the programming screens for the keys and fobs. The procedure went through without a problem allowing the engine to start so I could test drive the vehicle. With all the monitors “Ready”, I was confident that I had repaired the DTCs of the EVAP system and the O2 heaters. The customer’s car passed inspection without further incident.

Figure 2 Figure 3

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