How can you check the PCM to see if good /bad - Diesel Forum - TheDieselStop.com
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99 & up 7.3L Power Stroke Engine and Drivetrain Discussion of the 99 & up 7.3L Power Stroke diesel engine and drivetrain in the 1999-Up Super Duty trucks and Excursions. No gas engine discussion allowed except on transmissions and drivetrain that pertain to all models. Please confine discussion of topics in this forum to those items that are specific to the 7.3L Power Stroke engine.

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Old 03-03-2010, 06:35 PM   #1 (permalink)
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How can you check the PCM to see if good /bad

Is there a simple way to check to see if the PCM is good or bad? I have a 99 7.3 that won't start. Also, if the PCM were bad, would a scanner still pick up codes?
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Old 03-03-2010, 07:32 PM   #2 (permalink)
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if the truck doesnt start, the mechanics cant test it... my wife fried my pcm and there really was no way to test it...

the pcm/ecu regulates fuel... so if youre turning on the truck, and the wait to start light doesnt come on, then you turn the key and it just cranks and cranks... its not getting any fuel

the only way that i know to test it, is to find someone who has the same year truck you have and swap out his pcm and see if it starts...

this is just from my experience, i am no pro... i ended up buying a new one and it fired right up first try
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Old 03-03-2010, 07:50 PM   #3 (permalink)
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Unless the PCM is completely fried, someone with a compatible can tool can hook it up and check the PCM. When they go bad most likely it's just a few circuits that fry, and it may still spit out codes to tell you what's going on.

If your issue is just a no-start, then it's very likely that your PCM is fine.

What are the specifics of your no-start? Does the WTS light come on when you turn the key to on, and then go off as normal? If no WTS light, it usually means that the PCM isn't getting power. Check your fuses, and if #30 (30A) under the dash is popped, that probably means your fuel heater has shorted. So crawl up under the hood and disconnect the electrical connector going to the back lower portion of the fuel filter housing (leaving it disconnected), then replace the blown fuse and see what happens. The fuel heater isn't critical, and you can fix it when time allows.

Give us more info and we can help out.
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Hard or no-start? Check Here
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Old 03-03-2010, 07:51 PM   #4 (permalink)
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Thanks for the info. Unfortunately I don't know anyone with the same year I could try that with. How much was it to replace your PCM?
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Old 03-03-2010, 07:52 PM   #5 (permalink)
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you can indeed test the PCM using a multi tester and a diagnostic tree that is in Ford Service manual. It is not easy but doable. I have done a few but you need the diagostic tree to follow the procedure. Maybe someone can scan and post it or have a link
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Old 03-03-2010, 08:02 PM   #6 (permalink)
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No start 99 - need help
I posted the info below a couple days ago regarding my problem. I did check my GPR and it is not getting power to the GP's. I have also noticed that there isn't ant smoke when I turn it over, so I assume it is fuel related. I just don't know if it an electrical issue or not. Any help would be greatly appreciated.


My problem started several months ago with a stumbling problem only when it rained. It would occasionaly stall at a stop sign/light, but always restarted. Then it progressed to not starting when it was raining, but would start a day or two after the rain stopped. Now it won't start rain or shine. I have checked most of the things I found suggested in the forum to check, i.e. Fuses & relays, looked for water leaks/shorts, CPS(new), Batteries are brand new and crank very fast, HPOP level is fine, fuel pump is working(can't check pressure though), the glow plugs were replaced a couple years ago,(I have plugged the block heater in just to warm the motor in case they may have failed), unplgged the IPC and EBP. There isn't any smoke when it's cranking. Still no start. One thing that has changed during this is the WTS light use to come on for the usual lenght of time, now it doesn't come on at all. I did have a local mechanic run a scan with his Snap On Modis & it pulled P0603 & P0470. Neither of which sounds like would be the cause of the no start. Unfortunately this mechanic didn't know diesels or how to really use the scanner to diagnose one.

Can anyone help me or maybe know someone local that has and knows how to use a proper scanner? Unfortunately I'm not in a position to pay dealership prices to get it repaired.
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Old 03-03-2010, 08:07 PM   #7 (permalink)
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I think your IDM has water in it
Your PCM connector could also be getting wet
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Old 03-03-2010, 08:20 PM   #8 (permalink)
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Jim,

How would I determine if water is in the IDM? Isn't it a sealed unit? Also, if the PCM connectors got wet, wouldn't theydry out after a few days, or could that have caused damage to the PCM?
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Old 03-03-2010, 08:51 PM   #9 (permalink)
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First, you need a high-end scanner or diag system that can communicate with the PCM. Second, you plug in that scanner and communicate with the PCM. (I don't think reading codes is the same thing as communicating with the PCM.) If you can't communicate with the PCM, then your PCM is fried.

I don't know if the AutoEnginuity software and a laptop plugged into the port under the dash is "high end" enough. But I suspect it is. Otherwise, you need a $2,000 New Generation Star (NGS) or Snap-on tools scanner. Most programmer/tuners that can read codes, and the cheap scanners you can borrow from AutoZone, are not powerful enough to communicate with the PCM.
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Old 03-03-2010, 09:22 PM   #10 (permalink)
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If it is the PCM, you will need it programmed in the truck
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Old 03-04-2010, 03:37 PM   #11 (permalink)
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Quote:
Originally Posted by Trussell View Post
Jim,

How would I determine if water is in the IDM? Isn't it a sealed unit? Also, if the PCM connectors got wet, wouldn't theydry out after a few days, or could that have caused damage to the PCM?
I'm not Jim, but I can answer your question.

The IDM is "sealed" but it has a breather port on it that could let water in. I've seen quite a few that have had signs of water (corrosion) on the case and at the breather, so it's not out of the question for them to get wet.
The IDM is mounted behind the FX50 emblem on the driver's side, above the wheel well liner.

The PCM connector goes thru the firewall and is susceptible to spray. It's possible that it's getting water inside the connector and causing problems.

If you pull either one off, inspect for corrosion on the connector pins and evidence that the connector gasket is letting water in. When you put them back together, use some silicone dielectric grease at the gasket and a tiny bit at the terminals. Be sure especially on the IDM, that you wipe the excess off the face of the connector, or you may wind up getting pins shorted. I once goobered a bunch of dielectric on an IDM for a test and it threw a bunch of codes, including the "IDM failure" code. Took it back off and wiped the excess off, and it was fine.
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Hard or no-start? Check Here
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Old 03-04-2010, 07:56 PM   #12 (permalink)
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So is the IDM and the PCM enclosed in the samebox?
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Old 03-04-2010, 08:03 PM   #13 (permalink)
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So is the IDM and the PCM enclosed in the samebox?
No, they're completely separate.

The IDM is up under the fender. You have to pull the liner out to get to it.

The PCM is mounted in the cab by the parking brake pedal, with the connector end sticking thru the firewall.
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99.5 F250 PSD Supercab LB 4x4, ZF-6 w/SB Con OFE, 3.73LS, Boost & pyro gauges, Swamps S175/146 injectors, DP 80 HP Econo PCM (classic version), AIS, coolant filter w/"hokum" bracket, regulated return, heated mirror mod, lighted cupholder, Marinco heater plug-in.

Hard or no-start? Check Here
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Old 03-05-2010, 03:40 PM   #14 (permalink)
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I should be able to rule out the PCM and the IDM. I interchanged both of them in another 99 I found and that truck fired right up. Anybody have any other suggestions on what I could check out? I realize a scanner would be the best option, but I haven't been able to locate someone with one that can help me.
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Old 03-05-2010, 03:47 PM   #15 (permalink)
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One thing that has changed during this is the WTS light use to come on for the usual lenght of time, now it doesn't come on at all. I did have a local mechanic run a scan with his Snap On Modis & it pulled P0603 & P0470.
Went back and looked at your post. If the WTS light won't come on, it usually means that your PCM isn't getting power, although another cause would be that the WTS bulb is burnt out. Do the SES and other instrument warning lights come on as you turn on the key as they normally should?

The fact that you could get codes pulled means that the PCM has power, though.

The other thing is if you checked fuses, you should always check them with a multimeter. They can sometimes look good, but actually be burnt out.

Where are you located? There's surely another TDS member in your vicinity. You could also check the HELP NETWORK here: http://www.thedieselstop.com/faq/9497faq/registry/
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First truck -- 1929 Model A Ford pickup, restored from ground up. Wish I still had it!
99.5 F250 PSD Supercab LB 4x4, ZF-6 w/SB Con OFE, 3.73LS, Boost & pyro gauges, Swamps S175/146 injectors, DP 80 HP Econo PCM (classic version), AIS, coolant filter w/"hokum" bracket, regulated return, heated mirror mod, lighted cupholder, Marinco heater plug-in.

Hard or no-start? Check Here

Last edited by klhansen; 03-05-2010 at 03:50 PM.
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