How do I fix Check Engine Light - Bulb is Good

[ForcedTorque]

I am currently trying to fix a no start problem, and my CEL is not working, so I can't check my trouble codes. I have parted several MKIII's over the years, and have another cluster to rule out any problems with the cluster. The 92 cluster does have a little white box that screws down over the top of the 4 trouble lights, but I don't think it has anything to do with those lights.

The test cluster also did not help.

Also, my clock is not working in either cluster (2 different clocks).

While swapping out bulbs in the 92 cluster, I noticed that the board had heat in it, coming from the ABS light next to the CEL. I wouldn't call the heat too alarming, but thought I would mention it. It's not an LED bulb, so it could get warm enough to melt snow off of a traffic light.

I am assuming that I would follow the lines out of the 4 lights, and test for a signal in the corresponding plug. How much of a signal would I be looking for? And, I would need to know which pins to test.

How would I test the plug for the clock?

And, is it possible that these two things could be an a fuse together, without affecting anything else? I know, that sounds out there.

 

[ForcedTorque]

anybody? SME?

Please help! I also have found today that I am not getting power to the #3 terminal in my 6 pin igniter plug. Should I be thinking ECU?

 

[lewis15498]

My first guess would be multiple opens. What kind of shape is your harness in?

It could be the t1 or te1 wire is open, but then i would think your cel would turn on with key on and car off but not flash when bridged to check codes.

Edit: no that wouldnt make sense b/c of clock not working. I doubt it's ecu b/c of clock. Theres a pretty low chance the two are unrelated. Maybe damaged dash harness. Id find the tewd diagram then start testing the wires with the continuity function on a multimeter.

 

[RazoE]

what year is your cluster? I've heard about 86.5-1989 clusters not working on 90-92 cars...

and isn't the white box on the back for the boost gauge?

 

[toyotanos]

Don't think ECU, yet. It doesn't send voltage to the ignitor. I'm looking at the wiring diagram and what I see is that the voltage supply to the ignitor is the AM2 circuit (black-orange wire). This is one of the circuits that is controlled by the ignition switch, and it also supplies voltage to the ECU circuit. Start by checking the 30amp fuse marked AM2 and the 40amp fuse marked AM1. AM1 supplies the clock with power and it's also an ECU power supply.
What all works and doesn't work on the car? Is it only the engine control system and the clock?

 

[ForcedTorque]

Thanks for the replies guys. Bear with me, as I am no wiring genius. I can test for voltage and continuity, but I am a newb with those as well. I'll answer questions to the best of my ability.

My first guess would be multiple opens. What kind of shape is your harness in?

The harness is made for an 89. It was a year old when I installed it in my 89, and I put a couple of more months on it. I re-pinned it when I moved the motor over to the 92 body. I used the following link to do my re-pinning, and I learned a good bit of what I know since I started that thread.

http://www.supramania.com/forums/showthread.php?t=99311

It could be the t1 or te1 wire is open, but then i would think your cel would turn on with key on and car off but not flash when bridged to check codes.

From memory... Aren't these the 2 you jump to check codes? One of them is very hard to see any terminal in my diagnostic block. I continued on testing parts without checking codes, since the light doesn't even come on with the key. I would rather have the car starting before worrying about the light.

Edit: no that wouldnt make sense b/c of clock not working. I doubt it's ecu b/c of clock. Theres a pretty low chance the two are unrelated. Maybe damaged dash harness. Id find the tewd diagram then start testing the wires with the continuity function on a multimeter.

The TEWD would do me no good. I can't make heads or tails out of a simple electrical diagram. But, you think those two are related?

what year is your cluster? I've heard about 86.5-1989 clusters not working on 90-92 cars...

and isn't the white box on the back for the boost gauge?

The cluster is the original 92 5-speed from the car. I don't believe the box is boost gauge, but I can't remember where they went. It's upper 30's and raining outside, or I would go get it now.

Don't think ECU, yet. It doesn't send voltage to the ignitor. I'm looking at the wiring diagram and what I see is that the voltage supply to the ignitor is the AM2 circuit (black-orange wire). This is one of the circuits that is controlled by the ignition switch, and it also supplies voltage to the ECU circuit. Start by checking the 30amp fuse marked AM2 and the 40amp fuse marked AM1. AM1 supplies the clock with power and it's also an ECU power supply.
What all works and doesn't work on the car? Is it only the engine control system and the clock?

AM1 and AM2.......Are those in the engine compartment fuse box? I will check them tomorrow.

Here is a list of problems that I know of:

Check engine light does not work

Clock does not work

No Voltage to the #3 terminal of the 6 pin plug at the igniter. I'm now assuming this is why the car won't start. This has been found to be incorrect info. I was testing the wrong plug. I am getting 12 volts to the igniter.

There is a 2-pin plug near the igniter, that the housing does not match up. I removed the wires from the harness end, and I try to keep the two wires connected by dangling (only temporary/til I find a matching housing). I have no idea what that connection is for.

I have an Apex-i AFC-NEO wired into the harness. For some reason, whenever the battery is connected, it is powered on. After doing the re-pin, it was both the NEO and the fuel pump, but I swapped the two black/red wires in the B1 housing and the fuel pump cleared that problem. I tried to find a switched power to move the NEO to, but each one I found would work fine for switched power, until I started the car, and would then it would shut down. I put it back where it came from, and have been removing the negative battery cable since. I need to send the NEO back to Apex-i for the software update.

 

[lewis15498]

Seeing as the light never turns on, and the bulb is definitely good, i would say you have an open between the ecu and the cluster. Did the car sit for a while? maybe a hungry mouse got in there.

I will try and pull up the wiring diagram for it and have a closer look.

 

[ForcedTorque]

Yes, this was David Zamora's (FSTOY) old car. He owned the car for 6 years, and put about 4000 miles on it. It was always garage kept, but rats do get into garages. I believe he sold his motor out of the car over a year ago.

He had a large amount of gauges and such in the car when I bought it. Those that I did not want were cut loose, and sold off. Many things looked to be wired in sequence, and I did the best I could to remove all wiring that went to everything I took out. There was also an aftermarket alarm in the car, that a lot of wiring is still in place for. The control box for that alarm is on the back side of the kick panel, not yet in the car.

The car did run for about 50 miles, and was always kind of hard to start. It got gradually worse until it no longer would start at all. It will turn over all day long.

 

[lewis15498]

Ok first we gotta get the cel figured out.

The clock does not appear related to the CEL. This means one isnt causing the other, however the two could have the same cause ie chewed wires

Accordingto the TEWD diagrams it looks like it gets power from a 7.5A to it with a yellow wire. from the bulb it will have a grey wire with a green stripe that goes back to the ECU. Your gonna need a multimeter.

Here are your first two tests:

First were gonna test the yellow wire. Chances are theres more than one but they all do the same thing. so there is two things you can do, 1 test them all or 2 look at the back of the cluster and figure out which one it is by following the conducting lines on the back of the cluster to the plug. Set your multimeter to DC volts. with the key in the on position touch the red lead to the yellow wire (dont need to splice the wire, just touch the prong on the plug. touch the black lead to a solid ground (no paint or heavy rust). You should have voltage.

Second were gonna test the Grey/green wire for continuity. Set your multimeter to continuity, symbol should look somehting like this but all connected. " ->| " Your meter should say OPEN or opn or some shit. Touch the two leads together. When you do this it should say CLOSED or clsd something to that effect and may also beep. This is telling you you have made a connection between the two.
Unplug the ECU. The car need not be on for this test. Look at the ecu Plugs. You are looking for one with a Grey/grn wire. Again there may be more than one of these. To narrow your seach, you want one that is heading over to the cluster and not out to the engine. Also find the gry/grn wire that goes to the CEL. Touch one lead to the cluster pin and the other to the ECU pin. If you pick the right wire and there is a connection the meter will indicate closed (meaning closed aka complete circuit). If the wire is damaged the meter will remain at open (not complete circuit).

Do these, let us know what you find and we will take it from there.

 

[ForcedTorque]

OK, I did the two tests above.

Test 1 - No Voltage coming to the light = Fail

Test 2 - Grey/Green wire continuity = Pass

I pulled all of the fuses in the fuse box, and found one 15 amp Cig fuse blown. I replaced it.

There are a couple of changes that I noticed either before or after that. Before that, I noticed that my NEO no longer gets any power. After replacing the fuse, I also noticed a clicking under the hood when I turn on the key. That could have been there all along, but I have never noticed it.

 

[ForcedTorque]

I did find and test AM1 and AM2 this morning. It's finally dry enough to work on the car for a little while, and the wife is trying to drag me Christmas shopping. I think I have now performed all suggested tests.

I could not see through the window of either of these fuses. So, I pulled them both, and tested for continuity from one post to the other. Both of them passed this test. I tested this method on the blown fuse I found yesterday, and it failed on the known bad fuse.

I then pulled each fuse in the engine compartment fuse box, and found none blown there either.

I will be back later to do more searching.

 

[shaeff]

For shits and giggles, check the 7.5A IGN fuse in the driver's side kick panel.

 

[tbcmorris]

That was gonna be my suggestion also

 

[ForcedTorque]

For shits and giggles, check the 7.5A IGN fuse in the driver's side kick panel.

OK, I did the two tests above.

Test 1 - No Voltage coming to the light = Fail

Test 2 - Grey/Green wire continuity = Pass

I pulled all of the fuses in the fuse box, and found one 15 amp Cig fuse blown. I replaced it.

The IGN 7.5 amp fuse was one of those I checked, and found good yesterday. I did mean the fuse box inside the car when I posted that. Today, I checked all of the fuses in the engine bay fuse box. I even pulled the relay out of the box in the bay and tested resistance between post 1-3, and got a reading of about 68.5 out of it. I had another relay off of a dash harness, with the same part number, and it had an identical reading. I don't know how much resistance it should have, or what the specs are. They are either both good or both bad, but I figured with them identical, it was probably a good sign.

 

[ForcedTorque]

Update**********

I was fooling around with this a little more today, and found that I am getting 12 volts to my igniter. I had earlier stated that I was not, but I was testing the wrong plug. Yes, I am so stupid.

Also, my NEO is once again getting power whenever the battery is hooked up. This one is the least of my current worries, but could also be the root of them all.

So, current list of problems:

1. No CEL. Grey/grn wire is good from ECU to the cluster, but no voltage is getting to the light. This leads me to believe it has to be an ECU problem, and thus could solve all problems. Am I correct thinking this?

2. Clock in instrument panel has no power.

3. Car will not start! Hence the reason I started paying attention to the CEL. I have followed the TSRM to test almost everything on the car. I have not yet tested the TPS or done the 3 volt battery test on the igniter.

4. NEO gets power at all times. Would my car with the LEX/550 upgrade run much at all without it? I need to send it off for the upgraded software, and I somewhat suspect this to be a possible cause of all problems, including maybe shorting out the ECU. I did find the the grounds under the intake to be barely connected when I started chasing issues.

 

[lewis15498]

1. No CEL. Grey/grn wire is good from ECU to the cluster, but no voltage is getting to the light. This leads me to believe it has to be an ECU problem, and thus could solve all problems. Am I correct thinking this?

No, ECU is not causing the CEL problem. It turns the light on with ground complete. In other words power goes from the 7.5A gauge fuse which was good, to the CEL, and the ECU connects/disconnects the ground to turn it on/off.
The problem your experiencing is before or in the yellow wire as seen below. There could be lack of power to it (unlikely) or an open in the wire (more likely).
Here are your next two tests.
1) Turn key to on position. Remove 7.5 A gauge fuse. Set multimeter to VDC. Touch neg lead to a good ground and test the connector the fuse plugs into. One of these should have voltage.
2) Now that you have established which is power has voltage you now test the continuity between where the other prong of the fuse plugs into. Set multi to continuity, touch one lead to this cnnector where the fuse would go (one end of yellow wire) and the other to the corresponding pin on the cluster plug. You should have continuity here, if you dont there is an open (break) in this wire.

 

[ForcedTorque]

OK......

Test 1 - Found power at the lower end of where the fuse would be.

Test 2 - I think I understood to check the negative side (yellow wire) to the corresponding on the cluster plug which would go to the CEL. I'm lost on this test, because we have already established that wire in the plug to be Grey/Grn. I could not find a yellow wire in that plug. It appears that in the diagram that the yellow wire does turn to Gry/Grn, so I tested at that Gry/Grn spot, and DID NOT find continuity. But, remember, we found continuity in that wire, coming from the ECU. Somehow, I feel lost in this test.

 

[lewis15498]

There definitely is a yellow wire on the cluster plug. It is the same wire you would have tested in the first test I gave you back on page one. Find it and test it again.

It the first 2 tests I gave you you established there was continuity in the gry/grn wire. The problem is not there. Your now trying to find what went wrong along the yellow wire, because its no longer carrying power to the cel.

 

[ForcedTorque]

Lewis, I must thank you for all of your help, and patience. It is greatly appreciated.

You just cleared up my current confusion, and I must have been confused back then as well. I didn't remember checking a yellow wire, and I don't think I ever did. I tested for 12 volts at the gry/grn wire, and it was not there. I get like.013 out of it.

I just found the yellow wire, but it is in a different plug than the gry/grn. It does have continuity from the fuse negative, and I also got 12Volts out of it. This was while the fuse was laying on the floor?????

 

[lewis15498]

Lewis, I must thank you for all of your help, and patience. It is greatly appreciated.

You just cleared up my current confusion, and I must have been confused back then as well. I didn't remember checking a yellow wire, and I don't think I ever did. I tested for 12 volts at the gry/grn wire, and it was not there. I get like.013 out of it.

I just found the yellow wire, but it is in a different plug than the gry/grn. It does have continuity from the fuse negative, and I also got 12Volts out of it. This was while the fuse was laying on the floor?????

There are multiple yellow wires. chances are you picked the wrong one. Look at the back of your cluster. find where the CEL bulb is. There will be two contacts that you can follow back to a plug. Wherever those two go, are the two wires that your testing.