Everyday diagnosing and working on vehicles is a challenge, to say the least. Most days it’s a satisfying experience, but some days are a nightmare. We all have those days no matter how experienced, well trained, and how good you think you are. You’re going to get your butt kicked. Some vehicles just seemed to be possessed, where nothing you do goes right, or the vehicle still has an issue. To top it off if you have other important things going on in your life it makes your thinking process that much worse.
The month of February and into March had been the perfect storm of a personal nightmare for me. I had the TST Big Event that was coming up in the not-so-distant future. It’s usually a live event and doing it for so many years I got used to doing it that way. This year with the pandemic, it was a bigger challenge, as the TST Big Event had to be presented virtually. There was extra pressure in preparing for something presented so differently from normal. So tackling difficult vehicles became even more so as my attention was being pulled in multiple directions.
2012 Chrysler Town and CountryThe first nightmare was a 2012 Chrysler Town and Country 3.6L van. The customer complaint was that the vehicle would sometimes stall, and the check engine light would illuminate. My tech Bill connected one of our scan tools to the vehicle and came up with a P0480 “Cooling Fan 1 Control Circuit/Open” (Figure 1). At first glance it seems straightforward because it is a common problem on many Chrysler products. When the problem is intermittent it becomes difficult to pull the trigger on an expensive component (such as a totally integrated power module or TIPM), especially when an elderly woman on a fixed income owns the vehicle.
To make sure the TIPM was bad we had to test and not guess, so Bill put together his game plan for how he was going to proceed and test it. After many test drives, he still had not uncovered the problem. One of the first steps that Bill performed was what I’ve taught in my class for years —make sure the load is good by testing it first. Bill did just that and applied voltage and ground to the disconnected fan circuit. He found that it worked as designed and was not pulling excessive amperage.
His next step was to look at the wiring diagram and hook up the eScope to the terminals of the low cooling fan relay (while the engine was cold). He then monitored the signal as it warmed up (Figure 2). With the scope connected and the engine warmed up, the waveform confirmed that the relay was not receiving the command signal from the TIPM. There was no ground path being provided for the controlled side of the relay (Figure 3). Bill previously confirmed all the necessary voltage and ground supply as well as continuity through the load. The conclusion of his testing after multiple road tests (cool downs and warm ups) confirmed that the correct call was to condemn the TIPM. He concluded that the TIPM’s circuit board couldn’t complete the relay’s path to ground.
As Bill was working on this vehicle, he called me over and asked what I thought of the test results. As usual, Bill performed his due diligence and made the right call because the new TIPM confirmed the fix (Figure 4). With the new part installed and the vehicle test driven, all monitors turned "Ready" along with the vehicle passing the NYS inspection without a problem.
2013 Dodge DurangoOur next nightmare vehicle was a 2013 Dodge Durango 5.7L that had an illuminated MIL and a P0750 “Low/Reverse Solenoid Circuit” DTC. The vehicle was stuck in 3rd gear via limp-home mode. The first step was to review scan data and freeze frame to see if the information would shine further light on the problem.
Bill’s next step was to consult our service information. We used ALLDATA, ProDemand, MotoLogic and Identifix to see if there was any more information that could assist his diagnosis. After researching the different systems and reviewing the wiring diagrams, Bill located the correct pins and proceeded to perform the recommended test (Figure 5).
The test that was recommended by all the information systems specified a resistance test that had to be measured at the PCM connector. The specific resistance specification for a good solenoid is 1.7 ohms. With the computer connector removed Bill performed the test, finding that all the solenoids measured 1.7 ohms at the recommended temperature range.
Bill was perplexed by the test reading he performed. He thought that one of the solenoid readings would be different since the computer was throwing a DTC and was in limp mode. He shared the problem with me and got me up to speed on the test results. I am not a big fan of resistance testing in most cases, and this was one of those. I suggested to Bill to connect an amp clamp and scope the current to compare a good solenoid to the suspect solenoid. The comparison game is a good one to use since it is a direct comparison between a good and suspect component.
Bill proceeded to reconnect the wire harness connector to the computer so he could start the engine up and test the current draw of the solenoids. With two amp clamps attached to the eScope, he came up with the waveforms that told the whole story. After we review the results, Bill was still unsure if he should pull the trigger on such an expensive part. The reason he was thinking that way was that the recommended resistance test passed. I reminded him that the resistance test was not valid in this case since the dynamic nature of the current draw test revealed the solenoid was drawing 19 amps (Figure 6).
He knew that he was the tech who would be speaking to the customer and had to make the correct recommendation. Bill asked for my take; I believed it looked bad and there was a possibility that the wire could be shorted, but the more probable cause was that the solenoid was shorted internally because the current indeed “ramped up” (as inductors should).
I suggested to Bill how to confirm if the wire was good and the solenoid was bad. He would have to remove the wire for the high current draw solenoid and switch it with a known-good solenoid wire. If the reading from the suspect solenoid wire was good while energizing one of the other known-good solenoids, then the wire was not shorted. That would prove the solenoid was the problem.
There are so many different connectors that have different release mechanisms and along with the dirt and warpage, it becomes a big pain in the butt removing wires from a connector plug. With a bit of patience and time, Bill successfully removed the wires from the computer connector and switched the bad one to a good one. He took the wire from the high-drawing solenoid (19 amps) and moved it to another solenoid (low-current drawing, 7.9 to 8.5 amps) and did the reverse by installing the wire from a proper-working solenoid and on the high-drawing solenoid.
The results were that both the wires were confirmed good while the high-drawing solenoid was confirmed bad. Understanding the circuit and using simple logic nailed down the correct diagnosis. The circuit that was pulling the 19 amps was caused by a shorted solenoid, resulting in the DTC and limp mode. Our pinpoint test confirmed the actual problem was the solenoid. Bill was now confident to make the call to the vehicle owner and explain the problem, along with selling him the necessary repair.
With the owner’s approval, Bill removed the valve body, ordered a new one from the Dodge dealer, and installed it (Figure 7). After the installation of the new valve body, filter and fluid we rechecked the current draw from the same solenoid’s circuit. We found that the new solenoid current draw was 8.5 amps (Figure 8).
With the MIL extinguished and the vehicle out of limp mode, it was time to test drive the vehicle. After a few successful test drives, we were confident that the root cause of the fault was rectified and the vehicle could be returned to the customer.
2011 Nissan PathfinderOur next difficult vehicle was a 2011 Nissan Pathfinder 4.0L that came in with the customer complaint of the MIL on and a low-power issue. After connecting our scan tool, we uncovered one of the most common DTCs on a Nissan vehicle, a P0101 “Mass Air Flow Sensor Range/Performance” (Figure 9). Freeze frame indicated the following:
After reviewing the freeze frame information, Bill knew the next thing he should check was the condition of the air filter and the MAF sensor itself. After the inspection, Bill decided to check the actual volumetric efficiency (VE) of the engine using the eScan VE test (Figure 10). The VE test confirmed that the MAF was underreporting, so Bill ordered an OE replacement part from one of our distributors.
With the new MAF installed, the VE test was repeated and looked just about perfect. Although the engine may have been running great (Figure 11), the MIL was still illuminated, which would prevent the vehicle from passing an emissions test. After more research, Bill found that there was a TSB NTB12-051k regarding PCM Reprogramming for MAF code P0101. He performed the procedure that extinguished the MIL, but there was still a problem. With the MIL off, the vehicle was test driven multiple times trying to set the monitors to “Ready” only to come up with the same issue of “Not Ready.”
With a customer who was starting to lose faith, Bill thought that the next best thing was to drive to the Nissan dealer and purchase a new MAF. However, the part number on the new Nissan part did not match the original MAF that Bill had already replaced. The Hitachi sensor sold by the distributor as the OE part had a different part number than the dealer’s. This was a first for us. With the second new MAF installed, the vehicle was test driven again only to report the same results, monitors “Not Ready.” The pressure was on and Bill had to think fast.
He contacted the Nissan hotline, which told him to remove the battery cables with the key off and touch the cables together for a few minutes. This should reset the computer back to base settings. I always teach this very thing in my classes, but I add an extra step for safety. I advise connecting a 1 ohm 10-watt resistor in series with the battery so the computer capacitors can be drained slowly (rather than instantaneously, possibly spiking the computer and causing damage). Using the resistor is a preferred method that many OEs recommend for setting the computer system back to the base setting.
Like all of us, Bill is human and makes mistakes (thank goodness, not too often). We have all been there when we have other things on our mind, and we are not on our game. To Bill’s credit, he reached out for help that assisted him in diagnosing and repairing this vehicle. With the procedure completed, the three monitors that were not able to run before (and even after a dealer MAF was installed along with the PCM being programmed) were finally able to run. The OPUS IVS support line Nissan tech told Bill that they have documented this issue before and suggested to only use the MAF purchased from the dealer. They suggested verifying it is the same part as the one being replaced.
This was a lesson learned and one remembered. My diagnosis on any Nissan with a P0101 is to always check the basics first (including the MAF sensor itself), and check for a reprogramming TSB. If the vehicle has a TSB for reprogramming, it is the first thing I am going to suggest to the vehicle owner after I check the basics and the MAF. My experience has been that Nissan programming takes a while and there are certain procedures that you must follow after the programming is complete. Always RTFI (read the friggin’ information) and follow the procedure. One of those steps could be removing the battery cables from the battery lugs and installing the 1 ohm 10-watt resistor and leaving it connected for 15 or more minutes (depending on how many onboard computers there are). What this procedure does is bring everything back to the base setting and usually allows monitors to run and become “Ready” quicker. After that procedure was completed, Bill test drove the vehicle again and was able to get all but the EVAP monitor “Ready.” The EVAP monitor needs a few cold starts and warm-up cycles to complete. After all is said and done, the Nissan was able to pass the NYS inspection and returned it to the vehicle owner.
As usual, I hope these case studies are helpful in your current and future diagnosis. I would enjoy hearing your feedback. And in case you were wondering, the virtual 18th TST Big Event went well.