QuestionQUESTION: 2000 T&C LTD. With the Ignition switch in the crank position, the starter relay clicks whether your in PRND.
Is this correct?
ANSWER: Hi John,
There are four possible reasons for the safety interlock on the starter motor to not be working: the relay is defective, the wire that is needed to be grounded (by the interlock circuit) on the relay's actuation coil for it to click is shorted to ground all the time, or a PN switch inside the transmission that is operated by the vertical shift rod is defective, or the wire that connects it to the pcm is shorted to ground. First would be to check the relay itself to make sure that it isn't defective, so try switching it out with another relay in the box with the same part number.
Then check to see if the pin of the relay socket that is toward the center of the power box is shorted to ground as it sits. Then try turning the key to run and see if it is shorted to ground when trans is in a gear other than P or N, and finally check whether the brown/yellow wire from pin 10 or the trans range switch to pin 41 of the pcm is shorted to ground when the trans is in a position other than P or N (put a pin through the wire's insulation to connect to it). One of those tests will reveal where in the circuit you have the cause of your problem.
Roland
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QUESTION: Roland,
Your input has been very helpful. I gave you bad information. The relay DOES NOT fire in DR. It only fires in PN. All the relays fire when you turn ignition switch and I was feeling/hearing the other relays. Now I got my meter out and concluded that pin 85 on the starter relay floats until you crank, then it is grounded by the PCM to fire the relay.
I grounded pin 85 and problem goes away. So I also checked the Ignition switch and it is OK. Replacing the TRS is a difficult task and I would like to first check the connections at the TRS, the PCM and the Relay panel, but it all seems buried. Is there an easy way without a scan tool?
John
ANSWER: Hi John,
Pin 85 is supposed to float until you put the trans in park or neutral AND I suspect it will stay floating until you turn the key to the run position at which point it likely shows ground, and should continue to show ground when you try the starter position of the ignition switch. The pin 86 should show 0V until you try the starter position of the switch and then it should show 12v which comes out of the ignition switch. The combination of that 12v on one end of the coil along with the grounded pin 85 cause the coil to activate the starter. So check that set of actions first and let me know what isn't happening reliably. I gave you the trs wire and its connections in the first answer, if you want to check that part out. The only intervening part is the pcm which is responsible for grounding pin 85 as I described it.
Roland
Ps Thanks for the rating and nomination.
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QUESTION: Roland,
The grounding of pin 85 is what causes the intermittent cranking problem, when pin 85 floats no crank, no current flow across the coil until pin 85 goes low. There are connections between the relay pin 85 and the port on the PCM which you have previously referenced. The TRS looks like a 10 pin device buried in the trans and I assume the PCM processes those input to pull the port to grd when trans is in P or N. Are there separate outputs for for each trans position, ie PRNDL? Getting to the wiring underneath the relay panel looks like the panel needs to be removed and there are a large number of wires coming into the PCM. Do all the outputs from the TRS go to the PCM?
Thanks again Roland!
John
I am going to drive for a day or so with pin 85 grounded to verify the intermittent no crank is gone.
AnswerHi John,
No, each of the wires is from an individual switch but each switch is set up differently as regards which combination of gear shift positions close it. The one I referenced is the only one that goes to the pcm and it is closed in the PN settings, although P and N settings also close some of other 4 switch wires that go to the tcm that deal with range. There are four other wires that deal with the back-up lamps (2), speed sensor ground and trans temp sensor, the latter two going to the tcm. One pin is unused. So 6 of the 9 go to the tcm, 1 to the pcm, and 2 for the back-up lamps.
Do be careful to warn your wife about the safety interlock being defeated while you diagnose the issue.
I will be interested to know what you learn.
Roland
