The problem is not always what you think

June 2, 2015
Following a good diagnostic plan can ensure success, no matter what you encounter.

Typically when a vehicle comes in with a misfire, you use your diagnostic routine to find the problem. Most of us will interview the vehicle owner, give the vehicle a real good look over, maybe take the vehicle for a test drive, connect a scan tool to retrieve Diagnostic Trouble Codes (DTCs), check Technical Service Bulletins (TSBs) and look at a service information source. After following all the initial steps in your routine, you’re going to take a closer look at the scan data. Is the misfire DTC a P0300 (Randome Misfire Detected) or is it a specific cylinder  DTC? Our problem vehicle, a 2005 Ford Windstar, came in with a P0300 DTC, along with a few more specific cylinder DTCs. After reviewing the scan tool misfire data and Freeze Frame, we looked into Mode $06 data and confirmed that the engine was still misfiring. Now misfires are generally not that complicated of a job, but if your are thinking this vehicle was going to be a slam dunk fix, you'd be dead wrong.

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After confirming the misfires, we needed to find and confirm what was causing them. In my diagnostic routine, I always start with the basics. For misfire concerns, one of the first basic tests I perform is one often overlooked by most of the techs I train. The step I am referring to is a relative compression test that can be easily be performed if you have a scan tool that has this feature installed. Once the relative compression test is selected, you will be instructed to crank the engine over while the software calculates the mechanical condition of the engine. If you don’t have a scan tool that has this capability, you can connect your labscope to the battery positive and negative terminals while setting/coupling your labscope to AC volts, or by connecting an amp clamp to one of the battery cables following by disabling fuel and cranking it over for 20 seconds or less. If all cylinders pass, you have ruled out a mechanical problem that is causing a loss of compression. Installing a new mass airflow sensor, oxygen sensor, spark plugs, coils or any other parts for that matter will not repair a mechanical problem.

We covered our usual list of basics without finding an answer, so the visual inspection came back into play. When we took a closer look under the hood, we noticed that the cowl grill was loaded with leaves (Figure 1) and other debris. Take a guess what component is in the same area? If you said the Engine Control Module (ECM), you'd be right! We also found that the area around the ECM next to the strut tower looked damp. After further inspection, we decided to remove the cowl and found it flooded with water. As you can see from the picture (Figure 2), the water was finding its way into the wiring harness of the ECM We removed the connector to the ECM and found water drops on the terminals and pins (Figure 3), ultimately turning out to be the cause of our misfire problem. After cleaning all the leaves and debris from the cowl area, we blew out the wiring harness and th ECM connectors, then applied Stabilant 22 contact enhancer to the connectors and pins. After correcting what we had found so far,  we started up the engine and were rewarded with a smooth idel, free of misses. 

The next step was a test drive, followed by a rechecking for DTC, pending DTCs and Mode $06 misfire data to make sure we resolved the problem. We wanted to make sure that this problem would not reoccur, so we took one extra step — installation of a plastic cover over the ECM wiring harness. The cover will prevent water from leaking down from the cowl grill if the drains become clogged again. We suggested to the vehicle owner to make sure they check the cowl area for leaves and other debris on a regular basis. 

No heatA 2011 Dodge Nitro came in with a no heat concern, and that's something you do not want to experience during the abnormally cold winter we just had in New York. This Nitro only had about 30,000 miles on it, so the diagnosis and repair for this vehicle should be a breeze. With heavy snow and cold weather, the vehicle owner thought he would save time and bring the vehicle to the dealer in his neighborhood. The dealer suggested and performed a cooling system flush along with replacement of the blower resistor. The owner told us that the Nitro was working great for a couple of weeks before it stopped working again. When he called the Dodge dealer to inform them that he had the same problem he brought the vehicle in for they told him that they could recheck the vehicle next week. As you can imagine, this did not sit well with the owner, especially with temperatures down in the single digits. When its cold out, heat is not an option — it's a necessity. 

Since this vehicle owner had a good experience with repairs I had performed on his Range Rover, he traveled out of his way to bring this Dodge inm to my shop for repair. We checked the cooling system and found that it was working at normal operating temperature, along with the heater hoses that felt hot. When I went to change the blower fan speed, I noticed the blower was not working. I believed that this was the cause of the no heat problem. Maybe this problem was intermittent, so I turned the heat and blower on and off, trying to duplicate the problem. The owner provided me with the dealer invoice that had information on the cooling system service and a blower resistor that had been replaced. Since the blower resistor was replaced, we decided to start our testing there. The resistor is a sealed unit that has been a problem on Chrysler products, but the chances of both the original one and the replacement being bad is slim.

We started by checking the load first so we could eliminate that component and concluded that the blower motor was working as it should. We continued to check all the component wiring in the circuit to make sure that they were operating properly. During this procedure, we found a drop in voltage on the wire terminal connectors that were connected to the new dealer-installed blower resistor. I had my tech remove and install the harness connector a few times to make sure the connection was tight while cleaning the terminals at the same time. In addition, I had him apply Stabilant 22 contact enhancer to the blower resistor terminals. This simple step was all that was needed to restore blower motor function, proving that  following  a good diagnostic plan will lead to a successful repair and in this case, have heat when it's really needed.