Major Electrical gremlin
Logistics Pro
Joined: Aug 2009
Posts: 3,609
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From: Arizona
from the diagram it looks like the pcm relay must be closed in order for power to reach pin 86 of the idm relay which in turn closes the idm relay and sends power to the idm thru the dark green/lt green wire. I am getting dizzy now.
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Elder User
Joined: Aug 2015
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yes that's what I see as well. I can't figure out why the idm relay won't trip. shouldn't the fuse 22 have 12 volts? Why would mine be only 5. My batteries are good, charge them I between testing. So they are fully up.
Logistics Pro
Joined: Aug 2009
Posts: 3,609
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From: Arizona
I think you are seeing the vref or the 5 volts that the pcm uses for reference voltage. I think there should be 12 volts from the PCM relay side when the key is on. If you can be patient I will check mine tomorrow after work with a meter, it's late and I am hitting the hay now.
Logistics Pro
Joined: Aug 2009
Posts: 3,609
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From: Arizona
I think when the pcm relay closes it sends 12 volts to the PCM. When this circuit does not get the 12 volts I believe it stays at the 5 volts that the pcm sends out for reference to various systems. I could be wrong that's why I want to check my truck tomorrow.
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Elder User
Joined: Aug 2015
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Likes: 3
Still can't figure out why fuse 22 only has 5 volts, which is obviously why the relay won't trip. Power comes to the box by the large to battery line on the left side. 90% of the box functions fine, except fuse 22 and the idm relay.
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Elder User
Joined: Aug 2015
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If you mean way back when I thought I had the 80 pin signal. That was from the pcm to the fuse panel to trigger the idm relay. But since then we determined that the pcm relay triggers the idm relay which triggers the fuel pump etc. BUT, I'm only getting the 5volt reference signal from the pcm threw the pcm relay to fuse 22. Then to the idm relay that wont trip. Voltage is to low at 5volts. That's the mistery, why is there only the 5 volt reference. It appears the box may be fried inside preventing or grounding out that 12 volts to fuse22. The big power wire to the fuse box is good and 90% of the box is working. Just that one circuit to fuse 22 is not working, and its obvious that's my issue since all my dead functions correspond to that idm relay.
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Elder User
Joined: Aug 2015
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Not sure if this is a clue. I use the new pcm for testing since I don't want to fry mine doing testing. Were pretty sure the pcm is not the issue. So when I'm testing the pcm gets quite warm, even hot after about 15 minutes. I know its supposed to get hot, but all the heat comes from the bottom left corner of the pcm, looking down at the bolt side. I figured it would get all around warm, not localized like that. Thinking of that it kind of makes sense that half the pcm is not working because of the relay/fuse glitch, and maybe the box is melted inside causeing feedback to the pcm heating up the working side??? Do you think that might be a supporting clue to a fried fuse box. I'm contacting the wrecker that sent me the pcm to see if I can get the fuse box too. If its cheap enough I might just throw that at it to see if it fixes me up.
Logistics Pro
Joined: Aug 2009
Posts: 3,609
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From: Arizona
OK I just checked my truck and I have battery voltage (about 11.8 volts) at the top terminal of fuse 22 with the key on. At the bottom terminal (which leads to the PCM) I have about .45 volts key on (about 1/2 volt), 0.0 key off.
Now, let me ask you a few questions. Not wanting to offend you in any way only help you, but I do not know your meter skills so I have to ask a few questions.
1. First, are you using a digital volt meter?
2. Are you measuring from the fuse pin with one lead to a grounded, unpainted surface with the other lead?
3. Which terminal are you seeing 5 volts, top or bottom?
4. What range is your meter set to, or is it auto-ranging and are there any decimal points?
5. Are you sure you are making contact with the fuse terminal? Are you using a T pin or similar tool to get down in there? (see pic below)
Hoping to help you get this figured out.
Now, let me ask you a few questions. Not wanting to offend you in any way only help you, but I do not know your meter skills so I have to ask a few questions.
1. First, are you using a digital volt meter?
2. Are you measuring from the fuse pin with one lead to a grounded, unpainted surface with the other lead?
3. Which terminal are you seeing 5 volts, top or bottom?
4. What range is your meter set to, or is it auto-ranging and are there any decimal points?
5. Are you sure you are making contact with the fuse terminal? Are you using a T pin or similar tool to get down in there? (see pic below)
Hoping to help you get this figured out.
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Elder User
Joined: Aug 2015
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I am using a digital multimeter, and it does not have decimal points , just 3 "0"s and is auto range up 1000. So 5 volts reads 005. I measured across the two terminals, not separately to ground, and I used a pin to get in there. I will do it your way right now and add the info in this message. Ok, top terminal, and an outside ground is 4 volts, bottom terminal outside ground is 10volts, top terminal to bottom terminal is 5 volts.
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Elder User
Joined: Aug 2015
Posts: 535
Likes: 3
Do I not have voltage on the wrong side of that fuse? You have battery at top terminal I have it on the bottom, and your other terminal is basically off, and mine has 4 volts. Could there be a short in the board of the fuse panel.?
Logistics Pro
Joined: Aug 2009
Posts: 3,609
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From: Arizona
My apologies, in my rush to check mine when I got home from work I misread the directory, I was checking fuse 23. Just checked fuse 22 and my readings are more in line with yours, 12.2 volts from bottom pin to ground, about 7 volts from top pin to ground. My voltages are a bit higher but my truck sits with a battery tender plugged in. I think your voltages are in line for average batteries. When you turn the key on with fuse 22 removed do you get a lot of clicking from the other relays?