How To Know If You Need a Jeep PCM Replacement
The Powertrain Control Module (PCM) is the computer that controls most of your Jeep’s essential systems. The PCM controls the engine timing, the fuel to air ratio, the transmission, and the anti-lock brakes, along with dozens of other smaller functions.
When your PCM fails, it can cause you to lose fuel efficiency and possibly fail your state’s emission inspection. It can also lead to backfiring, difficulty starting the engine, rough shifting, and rapid wear and tear on vital engine components.
Common Symptoms of Jeep PCM Failure
Because your PCM controls many of your car’s systems, there are a large number of possible symptoms. The most obvious is if your code scanner is reading any code that begins with “P06”. These codes all identify specific PCM problems.
Other common symptoms include:
- – The check engine light is on
- – Your engine stutters or stalls
- – Gas mileage has inexplicably gotten worse
- – Your Jeep is shifting erratically or seemingly at random
- – Your Jeep has difficulty starting
The main reason people spend so much on PCM repair is that many people, even professional mechanics, often misdiagnose PCM problems as engine or transmission issues, and attempt costly repairs to those systems. You could buy several PCMs for the cost of rebuilding one transmission.
Worse yet, rough shifting and poor engine timing can cause damage over time, which means that the longer the problem with your PCM goes undiagnosed, the more you’re likely to end up spending on repairs down the road.
If you’re experiencing any of these problems, it’s a good idea to have your codes read before spending a lot of money on mechanical repairs. At the very least, you’ll eliminate a possible cheap repair option. At best, you’ll be able to repair or replace your PCM before anything else gets damaged.
Diagnosing the Problem
Even if your PCM is sending a fault code, the problem may not be with the PCM itself. It may be with the wiring harness. Perform a visual inspection of the wiring, and replace any corroded contacts or frayed wires. If everything looks good from a visual standpoint, follow up with a multimeter to make sure you didn’t miss anything.
Another common problem is if your battery ground has shorted out to the vehicle’s frame. Inspect your battery contacts themselves, too. Low voltage is a cause of many PCM faults.
Beyond that, it’s a good idea to perform other diagnostic procedures based on the exact error code you’re reading. We’ve written separately about several of these codes, in our PCM repair blog.
One common problem that affects Jeep PCMs – particularly PCMs for the Jeep Grand Cherokee – is poor soldering on the 5-volt power connection. If all other tests have failed, you can try re-flowing the solder. We’ll go over this process in the next section.
Repairing Your PCM
Repairing a damaged PCM is difficult for anyone who isn’t experienced with soldering on a printed circuit board. At Solo Auto, our dedicated technicians can repair your PCM and mail it back to you within 24 to 48 hours. Once you mail in your PCM, our technicians will assess the symptoms of your module, calibrate the codes, and conduct an internal and external inspection. Once repairs are made, we’ll test the unit to ensure its working correctly, update the programming codes, and retest the PCM before mailing it back to you.
If you are experienced in these kinds of repairs and are willing to take the risk and make the attempt yourself, here’s what you’ll need to do.
First, you’ll need a 60/40 rosin core solder. It must be rosin core, not acid core, since acid core solder can damage the circuit board itself. You’ll also need DeoxIT, or a similar non-corrosive contact cleaner.
Remove the two small screws in your PCM cover, and carefully pry the closing tabs open. Remove the small cover, and set it to the side. Then remove the larger cover, and turn it over. On one side, you’ll see an electrical connector that’s soldered on. Clean off any potting compound, and reflow the solder, applying as little new solder as necessary to do the job.
Make sure the solder flows from each pad to the connector for that pad, without touching any other connectors and causing a short. Be very careful while you’re doing this. Any damage to the copper circuits will permanently destroy your PCM.
Next, clean all the contacts with contact cleaner, and reassemble your PCM. Sometimes this method doesn’t work, but it’s effective in the majority of cases. If your PCM still doesn’t work, you’ll need to replace it.
Replacing Your PCM
When you’re searching for a replacement PCM, it’s important to keep in mind that PCMs are programmed for a specific make and model of vehicle. If you drive a 2007 Jeep Liberty with a 3.7-liter V6, you can’t use just any PCM. You can’t use just any Jeep PCM replacement. You need the PCM for that exact car. Solo PCMs has more than 100 Jeep PCMs for sale, so you can find exactly the version you need.
Most PCMs are plug-and-play, so installation is just a matter of disconnecting the power supply, removing the old PCM, and installing the new one. If you’d like a more detailed explanation, our PCM replacement guide explains the process.
How Can We Help?
If you have any questions about your PCM repair or replacement, contact us on our website, or call us at 888-848-0144. SoloPCMs specializes in automotive computers, and our technicians are always willing to share their expertise.