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P0600 Code – What Does It Mean & How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.


P600 Serial Communication Link Malfunction


P0600 means the ECU (Electronic Control Unit) has failed to connect to one of the myriad controllers in your vehicle multiple times.

Your vehicle coding a P600 means the ECU triggers the Check Engine Light on the dashboard and your ECU switches to failsafe mode. 

The failsafe prevents further damage and protects your vehicle due to a failed controller or component.

The ECU remains in failsafe mode until it detects normal operation from the malfunctioning controller or the problem is repaired.


Fortunately, there are only a few root causes for a P0600 error coding on your vehicle. Usually this error is caused by one of the following issues:

  • ECU is no longer functioning correctly or the ECU has failed completely
  • Low battery voltage
  • There is a short or poor connection in the ECU wiring harness


This is one of those issues that you will definitely notice problems beyond an illuminated check engine light. Your vehicle is going to run poorly, if it runs at all.

  • The Check Engine Light will be illuminated
  • ABS and Traction Control systems may display warning lights on the dashboard.
  • The vehicle idles rough
  • The engine fails to keep running and stalls out
  • Vehicle will not start, or does not start reliably
  • Transmission does not shift gears properly or fails to shift


This is not going to be a DIY fix by any means. The ECU is a critical system for any vehicle, and it will require careful troubleshooting to determine the cause of the error code.

Here is our process for diagnosing a P600 error code so that the problem is found and properly repaired the first time you bring your vehicle in for repair.

  1. The first step for our qualified technician is to connect an OBDII scan tool and pull the trouble codes,  including trouble code history and pending codes that are causing the Check Engine Light to illuminate. Here’s a great one we use daily
  2. Next, the technician uses the freeze-frame scanner function to collect data for every code to determine what conditions the vehicle was under when each code was triggered.
  3. After pulling freeze-frame data, all the codes are cleared and the technician takes the vehicle for a test drive to see if the symptoms recur..
  4. Once the initial test drive is complete, the technician makes a visual inspection of the ECU and all connections for damaged, worn, or loose components that could be causing the vehicle to code P0600.
  5. The technician checks the battery voltage to make sure it is reading at the proper level
  6. Next, the technician uses a multimeter to verify electrical continuity for power and ground circuits of the ECU.
  7. Finally, the technician will perform the manufacturer’s ECU testing procedure. This varies from vehicle to vehicle, but is a crucial component of proper diagnosis and troubleshooting.

Common Mistakes

The most common mistake automotive repair shops make is assuming the ECU is faulty and requires replacement when low battery voltage is the actual cause of the P600 error.

It is critical to follow a sound diagnostic procedure for P0600 trouble codes to eliminate any simple fixes or problems.

Replacing an entire ECU for a vehicle is an expensive and labor intensive process, and recommending an ECU replacement should not be taken lightly.

How Serious Is A P0600 Code?

A P0600 trouble code means there can be some fairly serious malfunctions with how your vehicle operates. Coding a P600 may cause intermittent and erratic symptoms that affect normal operation of the vehicle.

If the symptoms of a P600 code cause your vehicle to stall or fail to start, the only driving you should be doing is to take your vehicle in for repair.

With P600 code, the ABS system and traction control system can become disabled, making driving in poor weather or heavy traffic a bad idea.

What Repairs Might Be Necessary To Resolve A P0600 Code?

  • The entire vehicle ECU requires replacement (the worst case scenario)
  • Diagnosing and repairing the cause of the low battery voltage (An easy and fairly inexpensive fix)
  • Repairing or replacing the ECU wiring harness (Labor intensive, but not necessarily expensive)
  • Fixing poor electrical connections (time-consuming but not necessarily expensive)


Bottom line, if your vehicle is coding P0600 on a scan tool, it needs some serious TLC at an automotive service center to find and repair the issue.

When your vehicle’s onboard computer “brain” that controls the systems that make driving an enjoyable experience is failing to connect to some or all systems in your car, it’s a serious matter that needs prompt attention from a highly qualified technician.

In most cases though, low battery voltage or faulty wiring are the cause, and you should be wary of technicians or shops that recommend a complete ECU replacement.

P0600 Code – What Does It Mean & How To Fix It