Number 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 sec
Can you drive with P0600?
Severity: Fix promptly — drivability fault. Short trips at moderate speed only. If the car has entered limp mode (won't rev, stuck in one gear), have it towed rather than forcing it.
If you ignore it: Limp-mode faults tend to strand you, and several of them (misfires, throttle faults) damage other parts while you wait.
This is the #113 most common code in our top-150 library, in the idle & throttle control family (Powertrain system). Severity is Number Nest's editorial triage — if the light is flashing or the car feels unsafe, stop driving it whatever any page says.
What P0600 means
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.
Systems involved: engine control module (ECM/PCM), transmission control module, serial data line.
Causes, ranked by likelihood
| # | Cause | Likelihood |
|---|---|---|
| 1 | Internal module fault in the processor-to-processor link | most likely |
| 2 | Faulty module software (update available) | possible |
| 3 | Open or short in a dedicated serial line between engine and transmission module (e.g. Subaru) | possible |
| 4 | Low voltage, voltage dips or a poor ground or supply at the module | possible |
| 5 | Fault in the transmission module at the other end of the line | less common |
Check them in order — the list is ranked so the likely, cheaper causes come before the expensive part.
Symptoms you may notice
- 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
Misdiagnosis traps
- Replacing the part named by the code title without testing. The code reports a failed self-test; the cause list above is ranked so the likely, cheap causes are checked before the expensive part is condemned.
- Clearing the code and declaring victory when the light stays off for a day — the monitor that sets this code runs only under specific driving conditions.
(General diagnostic guidance for this code family — no code-specific trap is published for this code.)
How a good shop confirms it
- Confirm the code and record any companion codes — companions narrow the system fast.
- Inspect the affected components and their wiring/connectors for damage, corrosion and looseness.
- Test the top-ranked cause with live data or a multimeter before replacing anything.
(Standard diagnostic path for this family, labeled as general guidance.)
Repair options & costs
| Repair | Shop total (parts + labor) | DIY (parts only) | Difficulty |
|---|
No single repair is costed for this code — the fix follows the diagnosis. The Repair Cost Estimator prices 28 common repairs once you know which one this is.
OBDex repair data for this code rates the job difficulty hard with a typical labor time in the 1–4 hour range and DIY possible: see the guide above.
Frequently asked questions
How much does it cost to fix P0600?
There is no single fix — the code names a system, and the cost follows whichever cause on the ranked list proves out. The Repair Cost Estimator prices the common repairs in that system; diagnosis (often $100–$180, frequently credited) comes first.
Can I drive with P0600?
See the can-you-drive verdict above — it is based on the system involved and the cascading-damage risk, and it is our editorial triage, not a manufacturer instruction. If the light is flashing or the car feels unsafe, stop driving it regardless of any code.
Will P0600 clear itself?
If the fault was a one-off (a loose cap, a cold-start glitch), the light can go out after several clean trips and the code ages into history. A fault that is still present re-sets the code as soon as the car runs that self-test again — monitors run under specific conditions, which is why "it hasn't come back in two days" is not proof of a fix.
Will my car fail inspection with P0600?
In states with OBD-based emissions inspection, yes — an illuminated check-engine light or an incomplete readiness monitor fails the test regardless of what the tailpipe would show. C-codes (ABS) fall under safety inspection instead in states that have one.
What should I check first for P0600?
The first item on the ranked-causes list above — it is ranked likelihood-first for exactly this reason — plus the free checks: recent work in the area (connectors left loose are a classic), fluid levels, and the battery and grounds on electrical codes.
Where this data comes from
Code facts, causes and symptoms come from OBDex — an open dataset of independently authored descriptions of the standardized generic OBD-II codes (CC0 1.0, public domain; github.com/foerbsnavi/OBDex). The SAE J2012 document itself is copyrighted and is not reproduced here. Cost ranges are Number Nest's own US planning model: national parts and labor ranges cross-checked against the CarMD Vehicle Health Index 2026 published averages, with labor adjustable by the BLS OEWS May 2025 state wage index for auto technicians (occupation 49-3023) — a wage index, not a surveyed shop rate. Severity and can-you-drive notes are our editorial triage, not a manufacturer instruction.