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Diagnosing a no-start issue on a Chrysler Town and Country

Saturday, July 1, 2017 - 06:00
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Recently I was asked to meet a kind, older gentleman in our parking lot at the shop. This patient, old man wanted to speak with me regarding his 2008 Chrysler Town and Country. It seems he's been disappointed with the vehicle, as it has left him stranded several times here of late. I waited patiently as he told me quite a lengthy story regarding the entire history of this quirky failure.

What I managed to extract from him is that, very intermittently, the vehicle fails to start. I asked him what he meant when he says "won’t start." He made it perfectly clear that when the key was turned to the "START" position, the starter would engage momentarily and quit shortly thereafter. On many occasions, the battle to start the van would be on for well over an hour before the starter would remain engaged long enough to get the engine idling.  He summoned me to the parking lot to demonstrate the issue for me. Unfortunately, the issue could not be reproduced, and this was the root cause of his frustration. This van has suffered from this erratic malfunction for well over a year. He informed me that the starter has been replaced twice as well as six ignition keys, two ignition switches and even two batteries! In fact, this malfunction occurred so erratically, any previous repair attempt would seem to fix the vehicle, but a few weeks later, the strange symptom reoccurred to his dismay. I assured him that if I could reproduce the concern while performing a series of tests, I should be able to isolate the malfunction and rectify the issue. Little did I realize how elusive this gremlin was going to be.

I always want to know exactly how a system is supposed to work before I try to figure out why it isn’t working. Here, I learned that there were 2 modules in charge of the relay.

Start with a full system scan

I began my investigation with a DTC scan of the entire vehicle. To my surprise, there were absolutely none stored. After many attempts to reproduce the issue, I was disappointed to find that it cranked, started and ran each and every time I turned the ignition key to the "START" position. I inspected the vehicle for aftermarket components with no suspects to condemn. I then chose to research TSBs and search Identifix for any similar failures (I like to go this route, especially when I have issues duplicating a complaint). Unfortunately, there were no offerings for me in either inquiry. What to do next? I never feel comfortable pursuing an electrical issue unless I can reproduce a symptom of some sort, but basic tests like load testing of the battery and starting system are a must, especially in this case. Ruling out what isn’t wrong with the vehicle — early on in the diagnostic process — is just as valuable as finding the cause of the symptom the customer is experiencing. Both the battery and starter circuitry showed no signs of failure or of any contribution to the peculiar malfunction this kind fellow was experiencing, for such a long period of time. As the afternoon came to a close, the gentleman assured me I could have the vehicle as long as I needed, so long as he could have it back with a confirmed fix. Tomorrow would be another opportunity.

I arrived at the shop Wednesday morning before 7 a.m. Typically, vehicles with issues like the one will be evaluated after the morning rush. I turned the key to remove the vehicle from the workshop and to my surprise, the vehicle cranked for about 500ms before the starter ceased! I returned the key to the “Off” position and reattempted to start. The failure finally showed its ugly face.

Because the issue was so elusive, I thought the best course of action may be to capture the actual fault right at the source (the starter circuit, because it quits working) and work my way out of the hole. Looking at the wiring diagram, it’s easy to see that the starter relay is controlled by both the Totally Integrated Power Module (TIPM) and the PCM. It’s time to do some research. I have to educate myself on the functionality of this starting system as to avoid yet another misdiagnosis. To start troubleshooting at this point may prove to be a premature, costly mistake. It’s easy to feel unproductive if we aren’t hands-on working on the vehicle. Experience will show you that taking the time to devise a game plan and executing it will get you to the cause a lot more efficiently than rushing in without a plan of attack.

The TIPM energizes the starter relay coil by applying voltage to terminal No. 85. The PCM creates a ground path for the starter relay coil by driving the low side at terminal No. 86. Makes perfect sense. Two computers control the starter relay, one at either end, but how do the respective ECUs know what to do and when to do it? Surely, we aren’t done researching yet. We still haven’t enough information to determine the total system functionality. This required research of each individual component. Unfortunately, the description/ operation of the starting system as a whole was non-existent. Careful research was critical to solve this issue once and for all and without unnecessary part replacement.

Know what’s supposed to happen first

Not being familiar with this ‘08 Town and Country's total starting system functionality, I had to start researching at the beginning — at the turn of the key. The ignition switch is where I went. After all, I still couldn’t be sure if I was dealing with normal system operation during a security breach. Perhaps it was a "normal characteristic" to cancel starter operation?

As it turns out, the ignition switch is a lot more than just a switch. It's contained in another node known as a WIN module (or Wireless Ignition Node). This unit not only contains the ignition switch, but also stores info for the tire pressure monitoring system and queries the ignition key for the security system. The WIN has a self-contained ignition switch which is simply an input to the WIN. When the WIN sees the ignition switch turned to the "Start" position and the key is valid, it will communicate the start “request” on the CAN bus to the TIPM. The TIPM will then output a voltage signal to the starter relay and simultaneously send a start request on the same CAN bus to the PCM. The PCM will respond and supply a ground path for the starter relay! WOW — that is one busy system!

Figure 1

So now it’s time to build a game plan. I still want to begin my analysis at the high current side of the system (starter relay) where the work is performed. Although some may not agree with my initial test location, I know I experienced the starter energizing momentarily. The method to my madness is to capture what is "disappearing" when the starter ceases its operation. I will, at that time, determine which direction to head in from there. I want simple access to the circuit so I can gain a bunch of info for a small investment of time.  

I removed the relay and wrapped the individual terminals with very thin wire. The idea is to allow me to test the relay in its normal location. By leaving the relay in this position, I've eliminated the chance of poor terminal contact in the fuse box eluding my capture of the failure.

 Now, take glance at Figure 1. The red trace is located at terminal No. 85 of the relay (the TIPM side) and the yellow trace is located at terminal No. 86 of the relay (the PCM side). As you can see, there are three distinct events on either trace. The first displays a proper crank and start of the engine. I then shut the key off and a few seconds later, I cranked and the engine starts once again, without a hitch. If you look at the traces and imagine what is occurring, keeping in mind our test location and how the system operates, you can clearly see that the TIPM is supplying the voltage (red trace) and the PCM is supplying the ground (yellow trace). The third attempt looks a bit different. The yellow trace and the red trace have both been interrupted; the ground side of the circuit (yellow trace) has clearly risen/no longer being pulled low, and the voltage supply-side (red trace) drops off almost simultaneously.

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