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DTC codes / P06xx · Computer and output circuits / P0600

P0600Serial Communication Link Malfunction

P0600 indicates that the powertrain control module (PCM) has detected a failure in the serial communication link that connects it to other onboard computers or modules. The PCM monitors the data bus and sets this code when messages are missing, corrupted, or the link goes down entirely, meaning the modules can no longer share critical information.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyProfessional
AreaComputer and output circuits

Symptoms you may notice

  • Illumination of the check engine light or service engine soon light, often with no other noticeable symptoms
  • Multiple warning lights on the dashboard, such as ABS, traction control, or stability control, because other modules lose communication
  • The engine may start and run normally, but some accessories or features like the radio, climate control, or instrument cluster may act erratically
  • Intermittent no-start condition or stalling if the communication failure affects the engine control module's ability to receive necessary signals
  • Transmission may default to limp mode or shift harshly if the PCM cannot communicate with the transmission control module

Common causes, most likely first

  1. Damaged or corroded wiring in the serial data bus, including open circuits, shorts to ground, or shorts to voltage
  2. Faulty connector pins or terminals at the PCM or at another module on the network, often due to water intrusion or vibration
  3. A failed module on the communication bus that is pulling the data line down or sending corrupt messages
  4. Low battery voltage or a weak battery that causes modules to drop offline intermittently
  5. Internal failure within the PCM itself, though this is less common than wiring or module issues
  6. Aftermarket electronic devices improperly installed and interfering with the bus signals

How to diagnose and fix it

  1. Perform a thorough visual inspection of the wiring harness and connectors at the PCM and other modules for damage, corrosion, or loose pins
  2. Check battery voltage and charging system operation; a weak battery can cause communication faults, so load-test the battery and verify the alternator output
  3. Use a scan tool to read all modules for communication codes and check for stored codes in other modules that might indicate which module is offline
  4. Measure resistance and voltage on the serial data bus lines according to the manufacturer's specifications to detect opens, shorts, or excessive resistance
  5. Disconnect suspect modules one at a time to see if the communication link returns, isolating a faulty module that is dragging down the bus
  6. Repair or replace damaged wiring and connectors, then clear codes and verify communication is restored with a scan tool
  7. If all external checks pass, consult factory diagnostic procedures for the specific vehicle to test the PCM and replace it only if confirmed faulty

Common misdiagnosis traps for P0600

  • A weak or failing battery is one of the most frequent causes of P0600, yet many technicians replace the PCM first because the code points to a communication failure; always load-test the battery and check charging voltage before condemning any module.
  • The serial communication link can be disrupted by a single faulty module on the bus, so disconnecting modules one at a time is a reliable way to isolate the culprit without replacing expensive parts.
  • Aftermarket accessories such as remote starters, alarm systems, or plug-in performance tuners can interfere with the data bus and set P0600; check for non-factory wiring before assuming a factory defect.
  • P0600 can be stored intermittently due to poor ground connections at the PCM or other modules, so cleaning and tightening ground straps is a cheap and often overlooked repair step.
  • This code does not always mean the PCM is bad; in many cases, the root cause is a corroded connector or chafed wire in the harness, especially in areas prone to moisture or vibration.

Can I keep driving with P0600?

You can often drive with P0600 if the engine runs normally and only the warning light is on, but avoid long trips or heavy loads because the communication failure may cause stalling or loss of power assist. If the vehicle enters limp mode or multiple systems fail, stop driving and have it towed to a repair shop.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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