How to Fix the P0606 Fault Code

How to Fix the P0606 Fault Code

You go to start your car, and the check engine light is on. We’ve all been there.

So you own your own code reader, or you have a friend who’s a mechanic and you have the code read. It says “P0606”. That’s as helpful as a sharp stick in the eye.

Or is it?

We’re going to demystify this error code. More than that, we’ll explain how to diagnose the problem, and how to go about fixing it.

What is the P0606 Fault Code?

The P0606 fault code means that there’s an error with your power control module (PCM).

Your PCM is the computer inside your car that monitors all the vital systems. Basically, it’s the brain of your car. Every time you start the car, the PCM runs a series of checks to make sure everything is okay. Overall, it checks over 100 functions, including your automatic transmission, O2 sensors, and engine pressure.

It also runs a self-check, to make sure the PCM itself is working correctly. When the PCM detects that there’s an error with its own circuitry like a pcm processor fault, it returns the P0606 fault code.

What Does it Mean For My Vehicle?

How to Fix the P0606 Fault Code

A faulty PCM can be one of the most expensive car problems to fix. This isn’t because of the PCM itself, which isn’t outrageously priced, but because these problems are often misdiagnosed.

A faulty PCM can cause your transmission to stutter. This can start off as a minor problem, but can get worse over time as issues cascade and cause the problem to get worse.

It can also cause your gas mileage to drop. The reason for this is that the PCM controls your engine pressure and fuel to air ratio. When it fails, it can run the engine too rich or too poor, leading to bad mileage and potentially fouling the pistons.

When people come to their mechanic with a stuttering transmission or low engine pressure, the mechanic may replace the transmission or perform extensive valve work on the engine, only to have the issue continue to get worse. This leads to a lot of expenses over and above the cost of replacing the PCM.

The good news? You already know what the problem is, so you can avoid costly repairs on other engine systems.

The bad news? If you don’t fix or replace your PCM, the problems will continue to get worse and may cause damage to your engine or transmission. This will get expensive since you’ll need to fix or replace those parts as well as your PCM.

What Causes the P0606 Fault Code?

Fortunately, not all P0606 fault codes are caused by the PCM. There could be other reasons your PCM failed its self-check, and some of them are much less of a hassle than a failed PCM.

One of the most common reasons is frayed or corroded wires on the PCM itself. This can cause short-circuits or bad connections, leading to a P0606 fault code. The same thing can happen if the connectors on those wires are corroded.

Another possible cause is a faulty ground circuit. Like other PCM connections, this can be caused by fraying or corrosion. The issue may also be with the wiring to one of the 100-plus sensors the PCM is connected to.

Finally, there could be a problem with the control area network (CAN) bus. This can cause a P0606 fault by causing shorts or bad connections, similar to corrosion.

Whatever the problem, you’ll need to get it fixed as soon as possible. Bad connections may not mean there’s anything mechanically wrong with your engine, but they can cause your PCM to malfunction, leading to engine or transmission damage over time.

In rare cases, a computer glitch can cause the PCM’s firmware to fail. This is a software problem and not a physical problem, but it still requires attention.

How Do I Diagnose the Problem?

Diagnosing a P0606 code is simple on its surface, but more complex in execution.

The short version? You need to determine if the problem is your PCM or the wiring.

The long version? You’ll need to check all the wires connecting your PCM with other devices.

This means you’ll need to trace the wires, checking each inch for corrosion or other damage. Since the PCM connects to so many sensors throughout the vehicle, that’s a lot of wire tracing.

The main problem here is time. Sure, you can avoid buying a new PCM by finding the damaged wire, but generally, the juice isn’t worth the squeeze. By the time you trace a hundred wires, you could replace the PCM itself as many times.

For most people, the best solution is simply replacing the PCM.

The exception is checking easily-visible wires and the CAN bus. Because they’re exposed, these parts are the most common source of wiring trouble.

How Do I Fix the Problem?

Needless to say, this is a difficult problem to fix at home, although we’ve written guides on repairing or replacing your PCM in the past. The best method is to replace the wiring harness that connects your PCM to the CAN bus, then turn your car on and see if the code is cleared. If that doesn’t work, you’ll need to replace the PCM.

If you’re concerned about doing this yourself, you probably should be. It requires both mechanical and electrical knowledge, and failure can be expensive, since you’ll end up paying for your home repair, then paying again for a mechanic to fix it.

At SoloPCMs, we specialize in repairing and replacing PCMs. If you’d like an estimate, we encourage you to contact us using our simple web form. Alternatively, you can call us at (305)-387-7759. We look forward to hearing from you!

in How To, PCM Repair, Powertrain Control Module.

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