Engine/Transmission (1994 - 1998) Starter Relay in PCM?

[Texis]

Still chasing my starter / ign problems. I noticed on the schematic that there is a starter relay that appears to be inside the PCM. If so, is this relay serviceable?

Running out of things to check!

 

[GAmes]

Look again. It is in the PDC (power distribution center) the big box under the hood. Pages 8B-2 & 8B-10 in the FSM.

 

[Texis]

GAmes.. check your wiring diagrams, appears to be 2 starter relays (according to the diagram). 1 in the PDC and 1 in the PCM?

 

[BigPapa]

I only see one in my diagram:

 

[fest3er]

It's a fairly straightforward circuit. The ignition switch connects +12VDC to the clutch pedal position switch (or a jumper for automatic trans). The circuit then passes through the starter relay control in the PDC (pins 85, 86). Then it runs to ground (for manuals); or it goes through the park/neutral switch (for automatics) and to the PCM 'sensor' input, and then to ground. The PCM only senses the park/neutral switch position.

You only have a few things to check:

• PDC 50A fuse #10
• wire
• ignition switch
• wire
• clutch pedal position switch (or jumper)
• wire
• PDC starter relay
• wire
• maybe park/neutral position switch
• ground

Since you verified the circuit from the ignition switch to ground, that leaves PDC 50A fuse #10 and the wire from it to the ignition switch. If you can, measure the voltage on that wire at the key switch with the key on (should have B+ voltage), and with the key in 'start' position (should still have B+, but could be a little lower). If the voltage drops very low, there is resistance in the path that must be corrected.

 

[Texis]

A6 C1 "Park Neutral Sense switch" which is located in the PCM on your diagram, bottom left. In discussions with my electrical engineer "dial a friend" he believes that this is signaling the PCM that the engine is being started vs controlling anything, as fest3er stated.

Having traced, ohmed, DC volt checked EVERYTHING (relay, new Park/Neutral, ignition hot to the relay, BRN to the starter, etc) and here's current "narrowed down" scenario:
If the ignition switch is off the column and hanging by the wires, everything works fine.. fires right up. If the switch is installed in the column, everything works BUT the starter! This one is baffling to say the least. All the wires and connectors at the switch are good, in fact I can hold the switch in it's correct position next to the column and it starts. Not a switch grounding issue either as I have tested with jumper wires to the column. Grounded, or un-grounded the switch works fine AS LONG AS IT IS NOT INSTALLED! (3 screws to the column) There is no binding from the tilt release, etc. It cycles smooth when installed.. just no starter.

Bought a new ignition switch, same result... so I took it back.

Bout to drive me nutz. :-O I installed a direct starter hot push button last fall, and it always works but "it ain't right" LOL.

 

[Bob4x4]

Sounds like the ign key cyliner has broken and not actually turning the switch far enough.If you are not familiar with what they look like check a new one and compare it to yours,you may find a missing chunk-fairly common issue

 

[MLee]

And all the wires are good internally? Sounds like a break inside the insulation and when hanging you have a connection. Just my thoughts.

 

[fest3er]

And all the wires are good internally? Sounds like a break inside the insulation and when hanging you have a connection. Just my thoughts.

Like the wire to the VSS on the rear diff. Speedo was erratic for some time. Finally went looking and eventually found *one* wire broken inside the insulation. (By then, the insulation had begun to break, making it easier to spot.)

In Texis' case, that should be two wires to check: +12VDC and starter circuit wire at the switch. Alligator clips, resistance or connectivity meter, then gently stretch the wire; if broken, the circuit will open. If you have sensitive fingers, you can probably feel the break.

 

[Texis]

I'll check 12DCV at the ign (RED) and the relay trigger coming off the ign (BLU/YL) later today.. but I can't make it NOT function when it's hanging by the wires? No amount of twisting and pulling keeps it from starting. Only fails to start when mounted to the column. I'm also going to look at the key tumbler.

Signed,
Almost NUTZ.

 

[GAmes]

A6 C1 "Park Neutral Sense switch" which is located in the PCM on your diagram, bottom left.

A switch is not a relay. Nothing in the PCM carries the amperage a relay does.

 

[Texis]

GOT IT!!!!!!!!!!!!!!!!!!!!!! the truck now starts with the key LOL.

The ignition switch was bad. It worked fine out of the truck, but if you side load the flag, the start function dropped off. Apparently the flag can short the internal hot path. It was only 14 months old (O'Reillys) but they replaced it no charge. So installing the switch and turning the key was side loading the flag in the column, causing it to short out the start function.. which explains the whole ordeal.

Thanks for all the inputs, hopefully little exercise will help someone else some day.