P0600: Serial Communication Link

P0600 means a serial data link that the module relies on has failed. At Ford it is the internal link between the main processor and the monitoring processor ('quizzer') of the electronic throttle safety concept: if data cannot be exchanged or check bytes are invalid, the code sets within about a second (diesel: 5 s), usually with the check engine and wrench lamps and a throttle failure mode such as an RPM limit. Subaru (also sold as Saab 9-2X) uses it for the dedicated serial line between engine and transmission module. GM does not use P0600. Lost CAN messages from a named module are reported separately as U0100 and following. Before replacing anything: check battery, grounds and supply, look for a software bulletin, reprogram with a stable power supply, and replace the module only if the code returns.

Symptoms

• Check engine light, at Ford also the wrench lamp
• Reduced power or RPM limit (throttle failure mode)
• Harsh shifts or transmission limp mode where the line links engine and gearbox
• Other monitors such as the catalyst monitor do not run

Most likely causes

• Internal module fault in the processor-to-processor link
• Faulty module software (update available)
• Open or short in a dedicated serial line between engine and transmission module (e.g. Subaru)
• Low voltage, voltage dips or a poor ground or supply at the module
• Fault in the transmission module at the other end of the line

What to check, in order

Start with the simplest. You can tick off each step.

1. Check the battery and terminals, and read the codes from all control modules with a multi-system scanner
2. Identify which control module is not responding and check its fuses, power supply, and grounds
3. Disconnect add-on accessories, such as alarms or trackers, and read the codes again
4. Inspect the network connectors for moisture or bent pins
5. Measure the network's resistance and signal using the manufacturer's wiring diagram

Good to know

• Repair difficulty: hard
• It can trigger limp mode.
• It affects emissions.

What each character of P0600 means

• P: Powertrain: engine and transmission
• 0: Generic code: same on every make
• 6: Control modules and outputs
• 00: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0600?

Drive cautiously to a repair shop if the car is behaving normally. If it goes into limp mode or functions such as the transmission or stability control shut off, stay close and be prepared to stop.

What causes code P0600?

The most common causes are: internal module fault in the processor-to-processor link; faulty module software (update available); open or short in a dedicated serial line between engine and transmission module (e.g. Subaru).

Related codes

• P0606Control Module Processor
• P060AInternal Control Module Monitoring Processor Performance
• P0607Control Module Performance
• P060CInternal Control Module Main Processor Performance
• U0100Lost Communication with ECM/PCM "A"
• U0101Lost Communication with TCM

Sources

• law.cornell.edu: 13 CCR 1968.2
• fordservicecontent.com: OBD Operations Summary Gasoline 2020 2023
• newtonnet.co.uk: fordobd2012
• fordservicecontent.com: obd summary diesel 2023

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.