Starter relay location/possibly helpful video.

https://youtu.be/v594j6Bp21s?si=8Ag8dCzkTrP9CK77

Hopefully not ECU or immobilizer problem. Does CEL turn on and go out?

From what I've read, the immobilizer will allow cranking, but the vehicle won't start so I don't think that's it (still nothing at the starter). I have tried two different keys as well.

Today I swapped batteries with my 5th gen 4R (known good) and was able to start the 5th gen with this battery, same behavior on the 4th gen with the known good battery, so swapped back. I noticed more voltage drop than I think makes sense when trying to start though. Both batteries would drop to around 12.2v with the ignition turned to engage the starter, with no action at the starter.

I checked for voltage at the control wire on the starter and get nothing there, so it seems like the starter isn't being told to start. I need to put 12v on that and see whether the starter motor goes.

Just in case I have two marginal batteries, I also replaced the battery with a new AGM. It's charging up to full now, but I don't expect that to impact this issue.

Since the starter control will be tough to get it, I think I'll tackle the relay next and apply 12v to it via that. Ideas/feedback welcome! Thanks everybody.

Yes, put 12V to the starter signal terminal and verify it cranks. Then you can focus on the ignition switch and downstream wiring to the starter.

AuSeeker, you're a rock star. I missed this and it's exactly what I was looking for. I followed along and verified my starter is good by shorting the two relay pins closest to the driver's side fender. I checked for power at the inside 7.5a fuse and found 13v there, so ignition switch seems good.

Now for the last pin on the relay -- this is my issue I think. I checked voltage between the ground pin and that pin (so the two pins furthest from the drivers fender) while the ignition was turned to crank the starter, and found 6.5v. Second oddity, is that 6.5v stays there after the ignition switch is released, which I wouldn't expect. I think I should see 12v here -- can anyone confirm?

So at this point I'm looking for a wiring diagram showing how power gets here. From what is described here, that voltage issue could be a bad transmission interlock (N versus P makes no difference to the problem) or a bad ECU. I'd expect bad interlock to provide 0v. I've seen at least one post in my digging where a failed ECU showed low voltage on these pins, but I'm only guessing at this point that 12v is what I should see.

Thoughts and ideas welcome, and thanks again to AuSeeker for the video link.

Lots of good advice here. It seems to be electrical to me too. I have been fooled by corroded cables to starter from battery. And ground cables from battery to frame.

My experience was an internally corroded positive cable that carried enough voltage for lights but failed to carry starter amps.

If your whole starter ststem is original perhaps replacing inexpensive parts first makes sense.

Yep, definitely started there. All contacts have been cleaned and reconnected to the starter, and starter is verified good. It turns over when I short the appropriate pins at the relay. I need to figure out why the relay isn’t receiving appropriate voltage to trigger the starter. I’m leaning toward the ECU at this point.

Two other ECU bad indicators:

1. I get no CEL to verify it works when I turn on the ignition. Can anyone verify theirs light up momentarily without starting the engine?

2. Neither of my OBD2 readers will link. They get power, but can’t seem to find anything to talk to.

I don't know what the voltage should be at the relay....BUT in case the lower voltage you're seeing is correct, did you rule out that the relay itself is good or bad??

I do however know a relay is a switch, so power is not sent directly from the ignition switch to the starter, the relay does that, the ignition triggers the relay, since when you jumped the 2 pins together it made the starter engage, so you have the correct voltage to get the starter to function, the lower voltage could be what triggers the relay to connect/switch on the two legs to send power to the starter.

Try swapping out the starter relay with either a new one or even better another of the same type from the fuse panel, in the video it seems there are 3 right there together that all look to be the same, you'll have to look at the numbers on them to verify that.

Thanks,I should have mentioned that I swapped the fog relay with the start relay. Fogs work with the start relay, but no change with the starter. What I didn’t think to do is check the voltage used to trigger the fog relay since that’s working. On the list for today.

Wiring diagram and detail on starter cranking circuit attached. CEL should light and "prove out" when igntion switch is turned on - inspection procedure attached. Inspection procedure for ignition switch attached.

Attached Images

	T4R V6 Starter Wiring Diagram.pdf (22.0 KB, 21 views)
	T4R Starter Cranking Circuit.pdf (224.0 KB, 21 views)
	T4R MIL Circuit.pdf (65.6 KB, 19 views)
	T4R Ignition Switch Inspection.pdf (17.8 KB, 21 views)

Awesome Buckaroo, thank you!

Locations for Wiring Connectors, Junction Blocks and Park/Neutral Switch might help you.

Attached Images

T4R Starting Circuit Component & Junction Locations.pdf (393.0 KB, 26 views)

Ok, after reading through the documentation Buckaroo provided, I see those relay pins should be 9-14v. I confirmed that by checking the same pins for fog relay and they sit at battery voltage when on.

It’s ECU time. I’ll get it out this weekend and see if I can source a programmed replacement. From a quick look there appear to be two modules behind the glove box, left of the cabin air filter. I think the one I need to replace is nearer the air filter, but should be able to confirm with what Buckaroo provided.

Thanks again everybody!

Lots of work to do before we indict the ECU - don't know how much you have done.

Looking at the starting wiring schematic, I think Pin 5 on that relay housing should have battery voltage all the time. If it doesn't the problem is the battery, fuse (30 amp) or wiring. You can then check the voltage in at the 5 amp fuse after the ignition switch - you should see battery voltage when you turn the switch to start. If you don't, problem is upstream (switch or wiring). If that is good, check the voltage at the ECU in wiring harness Pin 12 and you should see battery voltage when you turn the switch. If not, problem is between Pin 5 on the relay housing and the wiring harness connector to the ECU. If voltage is good, check pin out voltage on ECU - Pin 8 - when you turn the key. I think it should be 5V - if everything up stream checks out and you do not see the 5V, then the issue is your ECU. FYI, never put 12V on any of those pins or signal wires coming out of the ECU - you can smoke it. I didn't look at the T4R Starting Cranking Circuit description I sent you when I wrote this post, I just looked at the wiring schematic but I would expect it to agree with the decision tree laid out in that doc. You should check it and see.

FYI, Pin 1 on the relay housing gets the signal from the ECU and I think it should be 5V (guessing but that is typical ECU signal voltage) when you turn the key if everything between the battery and the relay is OK including the igntion switch, park/neutral switch, two fuses, all the wiring & connectors and the ECU. Every troubleshooting decision tree includes a "replace ECU" at the end because it is the diagnosis of last resort but it is rarely the issue. It is great you have a multimeter and are doing the testing - that's the way it should be done to get to the bottom of this and avoid the cost and suffering of replacing good parts. Good luck and keep the updates coming!

Oh - I don't think I've seen it mentioned but you should move that gear selector back and forth in case that park/neutral safety switch is a little out of adjustment. Sorry - one of the first things that should be checked.