ECM not communicating?

JIMEL48

MEMBER
1996 TOYOTA TACOMA
2.7L
4 CYL
2WD
AUTOMATIC
130,000 MILES

I cannot retrieve codes as the ECM is not communicating with scanner. Swapped ECM relay with no change. There is no power (fuse is good) to the 7.5-amp ign fuse. All other fuses under hood and in cab receiving power.
Background: Truck would not start and repaired 2 loose wires in igniter and replaced coil three weeks ago and truck ran fine with no detrimental codes being thrown.
I went out to start the truck after sitting for a week and would not start. I suppose its a bad ECM or an electrical problem coming into the ign fuse. Any suggestions on how to proceed?

7 Replies

KEN L

MASTER CERTIFIED MECHANIC
47,536 POSTS

There are two grounds and one power which makes the data port work. I would check the OBD fuse in the fuse panel under the hood, and the grounds.

Here is a guide to help you check for power at the fuse:

https://www.2carpros.com/articles/how-to-check-a-car-fuse

Here is a video that can help fix it as well:

https://youtu.be/6Tlg3JmgNSQ?si=msZRjCkfj26L7lX-

I have included the ground and fuse location in the images below. Check out the images (below). Please let us know what happens.

Images (Click to make bigger)

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Thursday, August 15th, 2024 AT 10:25 AM

JIMEL48

MEMBER
32 POSTS

Hello Ken, thanks for your help and quick response.

Grounds at pins 4 & 5 tested good, no power at pin 16 in DLC.

10amp (OBD) and 15amp (EFI) in engine compartment receiving 12.5 volts. 15amp (ECU-IG) under dash receiving 12.5 volts.

Also, there is no power to the 7.5amp (IGN) fuse under dash regardless of whether I am cranking engine or not which makes me think that it is playing a role in this, but schematic seems to show a direct connection to Pin 16.

Could the igniter be at fault? I have had 2 wires there that have worked loose from the connector a couple times. I have tried to replace the plug but have not been able to find one.
.

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Friday, August 16th, 2024 AT 2:28 PM

KEN L

MASTER CERTIFIED MECHANIC
47,536 POSTS

Yep, the fact that the IGN 7.5 fuse does not have power can be the problem. Here a the wiring diagram which shows that power to the fuse is directly from the ignition switch. So, to tell if the switch is the problem and not the wiring let check for power at the blk/red wire out of the switch with the key on.

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

Check out the images (below). Let us know what you find.

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Saturday, August 17th, 2024 AT 8:39 AM

JIMEL48

MEMBER
32 POSTS

Hello Ken,
I have taken the bottom panel off and have access to ignition/key, however it looks like I am going to have to start taking things out to access fuse box wiring. Do I need to pull ignition/key to access black/red wire? Also have we determined the problem is either the wire or the ignition/key is the problem?

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Tuesday, August 20th, 2024 AT 9:06 AM

KEN L