Scope & Scan - Service Repair

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You can't fix it the old way

Repairing cars today requires computer savvy
Wednesday, August 5, 2015 - 07:00
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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.

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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 
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