Undercar - Service Repair

Search Autoparts/Motorage/Undercar-service-repair/

When the block to a successful repair is not a mechanical one

Friday, March 1, 2019 - 09:00
Print Article

Man-made problems can take many forms. Sometimes a man-made issue is caused by an honest mistake. Other times it can be caused by a faulty part. In some circumstances the fault could be the result of a substandard repair that was made quite some time ago. Some may even argue that every issue with a vehicle is a man-made issue since man made the vehicle in the first place…I digress.  Regardless, stepping back for a moment and re-assessing the situation is in order. Each situation will be different. These issues can be broken down into a few different categories. Let us explore them individually.

Story #1: Insanity

We need to remember the cliché definition of insanity: repeating the same action over and over again and expecting a different result each time. An example of this would be: “I replaced the Mass Airflow sensor three times, so maybe the fourth MAF sensor will fix the problem.” I experienced this exact issue on a Mazda. A shop was on MAF sensor number four in an attempt to resolve a low power issue. The fault was actually a restricted catalytic converter. Maybe, in this case, they should have stepped back and reassessed the situation. What is the likelihood of getting four faulty parts in a row? I agree that faulty “new” parts could be an issue. Technically this was not a man-made issue initially, but needs to be recognized none the less.

Moral of the “Insanity” story: If a part does not fix the issue initially, step back and review your diagnostics. Accept the fact that you are human and you may have made an error. Learn from the mistakes and diagnose the next one more efficiently.

Story #2: Common sense

I was called to a shop to program a Jeep engine control module. I consulted with the shop prior to my visit and confirmed that a used JTEC (Jeep Truck Engine Controller) could be made to work on this particular vehicle. When I arrived, the technician informed me that they had replaced the valve body in the transmission due to a solenoid DTC. The vehicle started and drove into the shop before the repair and now the vehicle does not crank. The TCM (Transmission Control Module) no longer communicates with the scan tool but all other modules, including the JTEC, do continue to communicate. The technician “followed the charts” and determined that the JTEC needed to be replaced. Also, poking my head under the vehicle, I noted the transmission pan was not installed.

Does this scenario raise some questions? The vehicle cranked and started before the repair so what changed? The scan tool communicated with the TCM prior to the repair but now does not. What changed? The kicker: the TCM does not communicate but the JTEC does… so let’s replace the JTEC? I am not quite sure why the technician came to such a conclusion.

The diagnosis was actually quite easy. Maybe it was because I showed up with “a fresh set of eyes.” Maybe it was just common sense. My approach was to attack the “new” no crank issue. Connecting a scan tool confirmed that the TCM did not communicate. The JTEC did communicate and the gear selector PID indicated DRIVE. It is a pretty safe bet that this is why the JTEC is not commanding engine cranking. Since the valve body had just been replaced, I chose to disconnect the connector at the transmission valve body. Lo and behold, I regained communication with the TCM. The customer was informed that either the valve body had an electrical issue or improper installation had occurred. The valve body was replaced with another unit and the issue was resolved.

Here are a few common sense questions we should ask ourselves: Why would replacing a valve body cause a JTEC to fail? Why would replacing a JTEC solve a communication issue with a TCM? Why did the vehicle start and drive into the shop and now it does not start after a transmission repair? Most importantly, why did this technician go down the proverbial rabbit hole? We have all gone down this path at some point in our careers. In hindsight, I think we can all agree that the heat of the moment clouded our common sense. When confronted with “the hole” step back and gather your thoughts.

Moral of the “Common Sense” story: If things do not make sense STOP. Step back for a moment and reset your thought process to avoid the rabbit hole. If it seems like something does not make sense then it probably doesn’t.

Story #3: Do not be a slacker

Quality repairs do many things: fix the vehicle permanently, please the customer, please the boss, improve shop profitability and more. However, cutting corners on a repair might be sufficient (not acceptable) in the short term yet catastrophic in the long term. Piercing a wire for example could cause corrosion issues in the future. I constantly pierce wires for testing purposes but I always make sure to repair the wire I pierced with some acceptable type of sealant or wiring repair. My point: make a QUALITY repair to avoid future issues and come backs.

Figure 1 - Testing ground at pin 4 of the DLC resulted in bright test lamp illumination.

Here is an example of a sub-standard repair that caused the customer to spend lots of time and money when they should not have had to. In addition, a logical diagnostic process led to an accurate diagnosis in the end. The vehicle in question is a 2001 Dodge Ram 1500 with a 5.9 liter engine. The vehicle would crank and not start. Also, a “no bus” message was displayed in the odometer. The customer replaced the engine control module with a used unit and was requesting programming.

Figure 2 - Pin 5 of the DLC has a voltage drop that can be seen due to the lack of test lamp intensity.

Initial inspection confirmed that the MIL did illuminate and the vehicle was cranking and not starting. A scan tool was connected and communication was attempted. Ironically, the engine started when cranked. Disconnecting the scan tool caused the vehicle to stall. Reconnecting the scan tool allowed the vehicle to start again and disconnecting it yielded the same stalling result.

Figure 3 - A jumper wire was used to provide a good ground to pin 5 of the DLC.

Knowing that there is one power pin, located in cavity 16 of the DLC, and two ground pins, located in cavities 4 and 5, got me to thinking: could the scan tool be providing a missing ground between pins 4 and 5? A DLC breakout box was then connected in order to test the ground circuits. First, pin 4 was tested with a test lamp (Figure 1) and it illuminated brightly. Next, pin 5 was checked (Figure 2) and the same result was not achieved. The test lamp did illuminate but with much less intensity. The next step was to confirm our suspicion of the scan tool providing a ground for the vehicle. A jumper wire was installed between pins 4 and 5 (Figure 3). As suspected the truck started and ran. Disconnecting the jumper, no surprise, again resulted in a stalling situation. Time to trace some wiring diagrams.

Article Categorization
Article Details
< Previous
Next >
blog comments powered by Disqus