[wchp]

Trouble Shooting ICM on a B5:
All, This is a first pass to get what we need to get this into the InfoSection.
Seems like 4-5 ICMs died the last few days with the onset of really cold weather and there were posts on each asking what the symptoms were and how to diag/test. That I am aware of this is the easiest way to check it. Any feed back or sugestions would be great before we ask Kenny Payne to move it to the info section.
RFC

Symptoms: Rough Idle, Solid or Flashing CEL
Locate the ICM
It is under the Air Filter Plastic Cover
Shown in place:

And then removed with arrow indication ICM location;

Remove the Two plugs on each side of the module by pressing down on the spring clip and pulling at the same time:

Using a Multi-meter set to measure Ohms, take one lead and touch the center metal pin (#3) on the Five Pin side of the ICM
Using the other probe check each of the 4 Output pins. The reading itself is not of particular importance as long as it is not 0.00.
Good Pin out reading:

Bad Pin out reading:

As the FETs themselves are not replaceable a bad reading on any one pin means you need a new module.

You will need to remove the two screws holding the unit in place to install the new one. When you do you will see some white grease. This is thermal grease used to transfer heat from the metal backing for the ICM to the heat sink on the air box. MAKE SURE you clean and then apply the heat sink grease that came with the replacement unit to these two surfaces. Failure to do so may result in premature thermal failure of your new ICM.
Costs for a replacement unit seem to range from $110.00 to $150.00 for a non Bosch unit and $220.00 to $320.00 for the Bosch OE unit.

I could not read the label after re-installing to cover over the Non Bosch unit so I skipped the designer element. To date I have not seen any posts indicating the non-OE units are in any way inferior to the Bosch unit.

 

[atomicalex]

Oh, hot dog. Great write-up.

Let's get this vetted and ready to move!

 

[Medrosje]

great post wchp

 

[DrivinAJetta]

Nice write-up. I was wondering: will the ICM give any warning signs before it goes? Or does it just suddenly die?

 

[wchp]

From the majority of the posts, it seems that you go to start it at some random point and the engine starts and idles rough and then the CEL comes on and starts blinking. In my instance, I had driven to a freinds house with no issues (7 mile 15 minute ride), shut off the car, 30 minutes later loaded the golf clubs in the trunk, started it and the symptoms presented themselves. I do not recall anyone posting about having issues while driving?

Anyone?

 

[upilogue]

Alternative ICM throubleshooting method

Based on my experience this weekend, measuring the resistance of the ICM pins did not reliably tell me that it was the ICM. A better method is to use the diode-tester in the digital multimeter, as posted here (http://tech.bentleypublishers.com/thread.jspa?threadID=6343)

Found a new way to check the ignition module. Since it's just a bank of transistors, a meter with diode check mode will do the trick. On the activation (5 pin) side, put the minus(-) on pin 3 and check to 1, 2, 4 & 5. On the output (4 pin) side, put the plus(+) on pin 3 of the activation side and check to 1, 2, 3 & 4 on the output side. None should be open.

In my tests, the resistance of pin #3 (5-pin side) and pin #2 (4-pin side) was shown to be markedly different than the others, but the diode test showed that all of them were good. And indeed, the problem was the coil pack on cylinder 1, not the ICM.

I have 84K on my '99 1.8T, original owner.