Engine computer replacement


I have a 1991 Dodge Ram Van 350 (one ton) and the time has come to replace the engine computer. It looks like a fairly easy job after getting a few other things out of the way, but I’ve found that things are never as easy as they look.

1 Take the wires off of the battery.

2 Move stuff for good access.

3 Unplug the big connector.

4 Remove old computer.

5 Install new computer.

6 Plug it in.

7 Install things taken off for access.

8 Hook up the battery.

What problems can I expect to find? Will the big plug self destruct when unplugging or when plugging to the new unit? Is this a job for the experts?


I did the same job two years ago, exactly as you described. There were no problems and you should not expect any problems to occur. Replacing the engine computer is as straightforward as changing a light bulb. Go for it, my friend!


Is this a time change item, or, do you have certain complaints with the currently installed one?


I’m not aware of any time change associated with the engine control computer. It is 16 years old and the van has 182,000 miles. the voltage regulator is in the computer and it went bad on a trip and was half way fixed for the rest of my trip. Then I put an external regulator on the system which seems to work fine even though the VR in the computer is bypassed. I thought I would replace the computer, which you have to do if the VR in it breaks, just so the darn CHECK ENGINE light would go off. It is always on and the codes say I have electrical system problems and something wrong with the torque converter lockup solenoid. the codes checked by the ignition key method are 12, 41, and 37. To read the codes I have to switch a couple of wires between the alternator and the regulator which is not too hard the way I have it wired up. I also wonder about the condition of the computer since the one part, the VR, went bad. My biggest concern is the big plug with all the connections breaking since it hasn’t been removed in 16 years. The van is a camoer van in superior condition, no rust, and runs perfectly except for the computer. I am reluctant to take it to the shop since a Dodge dealer and an independent tech could not fix it when it broke on the trip, and people at any auto shop would think I am nuts with the system I have set up just to make it run right, except for the computer. It took me a week to figure out the wiring, another week to find a good regulator, and another week to get all my weird wiring installed in a decent way.

Thank you SteveF and hellokit for your answers.


They used to say to be careful of static sparks or the computer could be wiped out. If the humidity is very low, wet the garage floor.


I remember the alternator problem Hambone.

By disconnecting the battery first you will have no trouble installing the replacement ECU. It is always a good idea to remove power first before working on circuits like that, as I’m sure you know. Some ECUs need to be programmed after they are installed to match the cars various options but I don’t think yours will need that due to the age of it.

Pleasedodgevan makes a good point about the awareness of possible electrical damage due to static discharge. By keeping your hands away from the ECU contacts and by touching a good metal ground point on the car chassis before you handle the ECU you will be pretty safe.


Thank you 'pleasedodgevan’and Cougar.
I will take your advice to heart when I attempt the change. As I said, I am happy with the way I have it but am afraid I might let other things go wrong by ignoring the CHECK ENGINE light. Whatever did we do before such lights?


I had some work done on an older Chrysler van and they disconnected and reconnected the computer. After that it ran poorly. I think the flexing of the cable with that big plug cracked insulation and the wires were inducing current into each other. I had to unwrap the cable and separate the wires, then it ran OK. So, the lesson is, don’t flex those cables much and don’t work on it if it’s really cold.


Whatever did we do before such lights?

We watched the gauge and checked the oil at every fill up. We should still be doing it, but I admit I don’t do it as often as I should.

Of course there is the fact that today’s cars are much more complex and there are many many more things that need checking.