Engine no crank - no start - possible code 12

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Engine no crank - no start - possible code 12

Postby corax » Sun Sep 13, 2015 1:34 am

I've been having some weird starting problems with my newly acquired '88 ST165 - intermittent no crank, sometimes it would crank but not start and then not crank anymore when turning the key, sometimes it would crank forever and not start, occasionally it would might crank and/or start but the CEL would come on with a code 12 stored (no STA signal, sets when the engine reaches 800rpm without the ECU seeing a starter signal).

So the first thing I did was spend 10 minutes pulling the starter relay and cleaning the contacts (even though they looked clean). Same problem.

So I replaced the starter. Same problem.

I did some research and found the START RELAY MOD. I wired a relay up with the coil being triggered from the original starter solenoid wire and the load side of the relay getting power from the starter cable lug so it could supply straight battery voltage to the solenoid - easy enough, though I don't generally like cheap band-aids. Now it would crank every time I turned the key, but it was 50/50 on whether or not it would actually start.

So I got to thinking. With my experience with other Toyota products from the 80's I should have remembered that there is a basic flaw with the starter circuit. The issue is that power for the solenoid goes through the ignition switch, through the relay, and then to the starter solenoid. The whole point of the relay isn't to supply power, it's to provide a break in the circuit to prevent starter operation if the clutch pedal isn't depressed or, in the case of an AT, the transmission isn't in Park or Neutral. Here's some copy/paste stitching of the starter circuit diagram for an '88 ST165:
Image
working from the bottom of the pic above: with the key turned to START 12V power goes into pin 4 of the ignition switch and out pin 1, it then goes into pins 3 & 4 of the starter relay providing power for the load and coil sides of the relay, depressing the clutch pedal grounds the coil which closes the contacts on the load side, power then flows to the starter solenoid. So, the issue is that Toyota engineers thought it was a good idea to send 10-15 amps through the ignition switch contacts (a pretty healthy arc when it makes contact). Over time, resistance builds in the ignition switch from contact arcing which reduces the voltage sent to the ECU and the starter solenoid. Eventually there's not enough voltage to engage the starter or for the ECU to recognize that the engine is cranking over.

On 4runners from the late 80's with an external starter relay in the engine bay, you can supply the load side of the relay with power straight from the battery so that the ignition switch only provides power to the relay coil. Like this, cut the wire going to pin 4 and take it to a clean 12V power source:
Image

That's not really an option on the Celica since the relay is part of the under dash fuse/relay box. So instead you can spend 30 minutes to clean the ignition switch contacts (or just replace the switch, I'm cheap + I like to fix rather than replace).

Remove the steering column shrouds and you'll see the ignition switch. Use a stubby phillips to remove the single screw that holds it onto the ignition lock cylinder (circled in the pic)
Image

This is the switch. Place match marks on both halves of the switch to make it easier to line up when you go back together. Using a small pocket flat blade screwdriver, carefully pry the white/grey cap off of it.
Image

This is the contact plate. Under the contact plates is a plastic piece, DON'T let it fall out of the cap, if you do, there are 2 tiny steel balls and springs that may go flying - they are the detents make make the switch "click" into each position. They can be reinstalled if they do come out. The arrow is pointing to the burned/pitted starter solenoid contact point
Image

This is the harness side
Image

Carefully remove both contact plates without letting the plastic piece below get pulled out of the cap. Wipe all the grease off both. I used some 400 grit sandpaper to shine up the raised contact pads on both copper plates, I has to put a tiny bit of elbow grease into the main pitted area for the starter solenoid to get it smooth again. In the pic, the tab on the inner diameter of the big plate goes to the 6 o'clock position and the tab for the small plate goes to 3 o'clock on the plastic piece in the cap. These plates are spring loaded in order to force them into contact with the harness side contacts. You can just barely see the detent balls at about 10-11 o'clock and 4-5 o'clock on the plastic piece in the cap.
Image

Reinstalled with a bit of dielectric or silicone grease on the contact pads to help the contacts slide and not wear the soft copper plates.
Image

Clean the harness side of the switch the same way: wipe off the grease, lightly touch up the contact points (I'm a bit more gentle on the harness side so I don't grind the posts down much). Align the match marks on the 2 halves of the switch and snap it all back together. Reinstall the switch and the column covers.

I haven't had an issue and now my engine cranks and starts every time I turn the key to START. Hopefully it works just as well for anyone else who tries this.
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Keith
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Re: Engine no crank - no start - possible code 12

Postby Awesome-Trac » Sun Sep 13, 2015 1:59 am

Awesome write up! I've only had starting problems before I put the relay mod in and so far so good! At least I know where to look if it progresses
-1988 Celica Alltrac (white) Sold
-1988 Celica Alltrac (black) new project
-1990 Corolla sedan (sky blue) totalled by my brother :(
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Re: Engine no crank - no start - possible code 12

Postby 88st165 » Sun Sep 13, 2015 12:38 pm

Great info! Thank you for taking the time to write such an informative post.
Red st165 - Garage Queen turned wannabe track rat
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Black st165 - gone
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Re: Engine no crank - no start - possible code 12

Postby corax » Mon Sep 14, 2015 11:03 pm

Thanks.

Just wanted to point out that, unless it's been damaged somehow, it's probably NOT the wiring getting brittle/damaged with age and that this problem can be fixed in about 1/2 hr with a phillips screwdriver and some sandpaper.
Keith
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Re: Engine no crank - no start - possible code 12

Postby AllBlackEverythings » Fri Nov 27, 2015 5:18 pm

Alright, am I missing something? This relay is under the two piece plastic shroud between the steering wheel & the dash/firewall right? I'm tryin to find this relay on my 90, & nothing looks like what I'm lookin for in the pictures. Am I doin some kinda dumb ass noobie ish?
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Re: Engine no crank - no start - possible code 12

Postby AllBlackEverythings » Fri Nov 27, 2015 5:19 pm

Here's the top...
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Re: Engine no crank - no start - possible code 12

Postby AllBlackEverythings » Fri Nov 27, 2015 5:27 pm

Nevermind.... I just realized that I need to take the plastic shround off the bottom of the dash. Which I can only find one screw up by the dash illumination adjustment knob & one other way down where it meats the trim that covers the tranny tunnel, near the gas pedal...
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Re: Engine no crank - no start - possible code 12

Postby AllBlackEverythings » Fri Nov 27, 2015 5:45 pm

Ok, so I figured out how to get the dash apart, but I still can't find the relay....
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Re: Engine no crank - no start - possible code 12

Postby corax » Sun Nov 29, 2015 2:13 pm

AllBlackEverythings wrote:Ok, so I figured out how to get the dash apart, but I still can't find the relay....


The part that you'd be cleaning contacts on is the ignition switch, should be on the back side of the ignition lock cylinder. The starter relay is somewhere else (on my ST165 it is just forward of the fuse box in the driver's footwell)
Keith
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