OBD 1 Code 18
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Mountain Pass
Joined: Jul 2012
Posts: 116
Likes: 0
OBD 1 Code 18
Hello all! I am the proud owner of a 1986 Bronco XLT 302 EFI. Chasing down some gremlins the other day and pulled the codes. I found one lonely code, 18. I made sure the SPOUT jumper was good and connected and that it was not grounded. I then checked continuity of the IDM from TFI to ECM. It is showing only 60 ohms of resistance. Shouldn't it be 22k? Do these resistors ever fail by shorting? If it did fail by shorting, I would assume that this would turn my ECM into mince meat. Let me know y'alls expert opinion!
Hotshot
Joined: Jul 2020
Posts: 10,519
Likes: 2,654
From: Near Salt Lake City
You need to replace your TFI module
It's the ground circuit that melts the thick film and makes the bubble on the IC
(I've taken thousands of these TFI modules apart)
With all the recalls and crap we had to do like inspect the build dates on the modules
We learned the fault (ground circuit failure) and code 18 is the result if there is any code at all
Yours has not died unexpectedly yet?
Good luck
Many people relocate that module and the newer ones have the module under the drivers side hood hinge
Keep one of these in your glove box
It's the ground circuit that melts the thick film and makes the bubble on the IC
(I've taken thousands of these TFI modules apart)
With all the recalls and crap we had to do like inspect the build dates on the modules
We learned the fault (ground circuit failure) and code 18 is the result if there is any code at all
Yours has not died unexpectedly yet?
Good luck
Many people relocate that module and the newer ones have the module under the drivers side hood hinge
Keep one of these in your glove box
FTE Legend
Joined: Jun 2006
Posts: 31,930
Likes: 1,499
From: Ottawa, Ontario
Does the distributor have a grey or black ICM on it? It should be grey, parts stores will tell you the black module superceeds the grey but that is incorrect, there are internal electrical differences that make the black module incompatible with your truck.
Fleet Owner
Joined: Oct 2005
Posts: 20,789
Likes: 1,753
From: Kentucky
We had a very similar thread on Code 18/212 recently: https://www.ford-trucks.com/forums/1...-332-help.html
Short answer is the IDM circuit was open. The 22K ohm resistor can go bad, sometimes broken, or many have found bad solder joints at the splices. If you go the route previously suggested to change the Ignition Control Module (ICM) without verifying the IDM circuit you may end up with the same issue.
A diagram from the linked thread is below for reference.
A quick check with a DVM set to ohms will point to which direction to go.
Short answer is the IDM circuit was open. The 22K ohm resistor can go bad, sometimes broken, or many have found bad solder joints at the splices. If you go the route previously suggested to change the Ignition Control Module (ICM) without verifying the IDM circuit you may end up with the same issue.
A diagram from the linked thread is below for reference.
A quick check with a DVM set to ohms will point to which direction to go.
Hotshot
Joined: Jul 2020
Posts: 10,519
Likes: 2,654
From: Near Salt Lake City
The module is the fault of the IDM circuit
Not the other way around
It has been my experience for code 18
Replace the module problem solved
You could chase your tail for a while as I often do
Ohming out wires and such
I have seen bad splices and bad resistors
Very few and far between
Not the other way around
It has been my experience for code 18
Replace the module problem solved
You could chase your tail for a while as I often do
Ohming out wires and such
I have seen bad splices and bad resistors
Very few and far between
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Fleet Owner
Joined: Oct 2005
Posts: 20,789
Likes: 1,753
From: Kentucky
I have seen several in recent past where the root cause for Code 18/212 was the IDM circuit on the 1993 and earlier trucks and not the ICM. Given the cost of Ignition Control Modules (ICM) these days a few minutes with a meter is worth my time. Your mileage may vary.
Thanks for the input so the OP can choose which way they want to go to correct the problem.
Update:
Re-reading the OP's problem statement it does look like they did measure the IDM circuit. I assume the key was in the Off position when doing so. At 60 ohms that is a very low resistance. Where were the meter leads placed when the circuit was tested? A quick test would be to disconnect the ICM then remeasure again. If the resistance is good now then you do have an issue with the ICM.
Thanks for the input so the OP can choose which way they want to go to correct the problem.
Update:
Re-reading the OP's problem statement it does look like they did measure the IDM circuit. I assume the key was in the Off position when doing so. At 60 ohms that is a very low resistance. Where were the meter leads placed when the circuit was tested? A quick test would be to disconnect the ICM then remeasure again. If the resistance is good now then you do have an issue with the ICM.
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Fleet Owner
Joined: Oct 2005
Posts: 20,789
Likes: 1,753
From: Kentucky
Where are you referring to IDM? Pin 4 of the PCM?
Assume the truck runs, but you have this annoying Stored Code?
Have you cleared the Stored Codes then ran the truck through a drive cycle and re-ran the KOEO tests and Stored Code display?
Assume the truck runs, but you have this annoying Stored Code?
Have you cleared the Stored Codes then ran the truck through a drive cycle and re-ran the KOEO tests and Stored Code display?
Fleet Owner
Joined: Oct 2005
Posts: 20,789
Likes: 1,753
From: Kentucky
If the IDM circuit is measuring the correct resistance then I would start looking at the computer (PCM) as the culprit. But now you are at the crossroad of the cost of a new Motorcraft ICM versus a replacement ICM. Since the IDM circuit appears to be good and you stated you verified the SPOUT circuit is not grounded it's a toss up of good signal feedback/bad computer or the ICM is on the weak side which could cause your running issue(s).
At the very least pull out the computer then open it up to see if there are any burned components/traces or leaking capacitor(s). If it looks good then to me it's a toss up for which direction to go. My experience with Code 18/212 on 1993 and earlier trucks has always been caused by an issue with the IDM circuit itself. Others have very different experiences.
At the very least pull out the computer then open it up to see if there are any burned components/traces or leaking capacitor(s). If it looks good then to me it's a toss up for which direction to go. My experience with Code 18/212 on 1993 and earlier trucks has always been caused by an issue with the IDM circuit itself. Others have very different experiences.
Thread Starter
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Mountain Pass
Joined: Jul 2012
Posts: 116
Likes: 0
I ordered some new injectors that had come in, so I decided to go ahead and install them. Upon finishing the job, the truck runs like a top! Not sure if is was a severe vacuum leak that was fixed in the process, or the old injectors that were jacked up, but the problem seems to be solved. I will clear the codes, run it for a while then pull them again. Thanks for all of the input!
5th Wheeling
Joined: Feb 2025
Posts: 38
Likes: 2
If the IDM circuit is measuring the correct resistance then I would start looking at the computer (PCM) as the culprit. But now you are at the crossroad of the cost of a new Motorcraft ICM versus a replacement ICM. Since the IDM circuit appears to be good and you stated you verified the SPOUT circuit is not grounded it's a toss up of good signal feedback/bad computer or the ICM is on the weak side which could cause your running issue(s).
At the very least pull out the computer then open it up to see if there are any burned components/traces or leaking capacitor(s). If it looks good then to me it's a toss up for which direction to go. My experience with Code 18/212 on 1993 and earlier trucks has always been caused by an issue with the IDM circuit itself. Others have very different experiences.
At the very least pull out the computer then open it up to see if there are any burned components/traces or leaking capacitor(s). If it looks good then to me it's a toss up for which direction to go. My experience with Code 18/212 on 1993 and earlier trucks has always been caused by an issue with the IDM circuit itself. Others have very different experiences.
Fleet Owner
Joined: Oct 2005
Posts: 20,789
Likes: 1,753
From: Kentucky
Code 18 is probably a real error since the engine is dying. A quick check with a meter will verify the IDM circuit is good or bad. Either way I doubt it is causing your stalling issue. Start the engine then start wriggling wires. Not sure if the ICM/TFI wires are inside a foil sheath like the 1992 and up truck are, but that shield is known to wear through the wire insulation and cause issues.