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There is no sub forum in ETCG for interesting diagnosis, so I will post one here:
I suppose it is a sign of the times and current automotive complexity when you have to drop the transmission pan to correct a no start. The vehicle is a 2016 Suburban, but could happen in many electronic controlled transmissions. Multiple codes and no communications with ECM, BCM, etc. The no comm prevented the starter from being engaged as well as most everything else.
Before the no start, there had been many different episodes of various codes and failures.
A quick check of the DCL indicated 120 ohms which means a break in the high speed LAN resulting in only one of the resistors having electrical connection, disconnecting one of the terminating resistors. After starting in the middle of the chain and working toward the open, resulting in taking apart many things for access I homed in on the transmission. Although they call it a control actuator assembly which is inside the transmission, for all practical purposes, it is a TCM, since it has a CAN connection. Raised it and got under to check the Trans connector. I pulled the connector and was surprised at the splash of ATF. Removing the connector should not result in loss of fluid. Before removing the connector I observed that the plastic lock tab had greasy fingerprints. This is a 10K mile vehicle. I then pulled the trans pan and correctly installed the connector sleeve with new seals, locking the tab in place that is inside the oil pan, and checked the connector to see 120 ohms in both directions indicating that the control actuator was the break in the network chain.
It is necessary to drop the pan in order to properly lock the trans connector sleeve. After putting it back together, providing an unbroken network. it started normally and everything worked properly. I cleared the codes, test drove and checked for leaks.
SO… Who would have ever thought that we would reach a point in auto technology when you partially disassemble a transmission to correct a no start. The neutral safety switch was an issue for decades, but this one is something deeper than that. Modern technology is a little different than some switches and contact points.
Hope you enjoyed it.
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I love Diagnostic work myself. Just finished a Porsche that other people could not figure out. Car was 30 years old and injector plug has 12v to both pins so odd engineering still continues today.
The ECT value is examined in many different cases by the ECM logic. I expect that the difference between the ECT and IAT or some other thermal parameter under certain situations is not satisfying a logic condition of some description.
Wait until the suburban needs a new trans and the person who install it doesn’t know the tcm needs to be flashed and it shuts down other modules because serial numbers don’t match.
Yeah mule that would be a curve ball for someone who didnt know about the TCM. I would like to think that by now the trans shops would be aware of this, but I am sure your scenario has played out with someone by now.
[quote=”MBDiagMan” post=172229]Yeah mule that would be a curve ball for someone who didnt know about the TCM. I would like to think that by now the trans shops would be aware of this, but I am sure your scenario has played out with someone by now.[/quote]
Probably not an issue for the shops more of a message to the DIY person who may think replacing a trans is a matter of just putting a new or used one in.
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