P0600
PowertrainSerial Communication Link Malfunction
More often than anything else, this comes down to a tired battery or a poor connection upsetting the data network rather than the ECU itself dying. P0600 is the engine control module telling you it can't talk properly to one or more of the other modules on the car, usually over the CAN bus. When voltage drops or a connector goes high-resistance, the modules stop chattering cleanly and the ECU flags it. Treat it as a communication and power problem first, not a reason to panic about a new ECU.
ⓘ Information only. This page provides general educational information about fault code P0600. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P0600 mean?
P0600 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Serial Communication Link Malfunction.
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • Engine warning light on, almost always with a handful of other codes sitting alongside it
- • ABS and traction control lights popping up together, sometimes with the speedo dropping to zero
- • Car drops into limp mode with the throttle feeling dead
- • Intermittent starting, where it cranks fine one morning and refuses the next
- • Stalling at idle or a rough, misfire-like run on some cars
- • Gearbox shifting oddly or the instrument cluster going haywire on certain models
Possible causes
Causes commonly associated with P0600, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Weak or flat battery dragging system voltage down. This is the number one cause and the first thing to rule out
- 2. Corroded or loose harness connectors at the ECU or other modules, common on older VAG and Vauxhall cars where damp gets into plugs
- 3. Damaged CAN bus wiring or a connector that's worked loose, often after bodywork repairs or accident damage
- 4. Poor earth points to the ECU or other modules, which mimics a comms fault perfectly
- 5. Internal fault or software glitch inside the ECU itself, less common but it does happen
- 6. A failing module elsewhere (transmission, ABS, body control) that's pulling the whole bus down
- 7. Short or open in the data bus wiring, usually from chafing against a sharp edge or rodent damage
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Read every stored code on every module, not just the engine. The supporting codes usually point straight at which module has gone quiet, so a U-series code like U0100 tells you a lot more than the P0600 on its own
- 2. Load test the battery and check charging voltage. Anything below about 12.4V resting or a charging system that dips under load can throw this code by itself
- 3. Inspect the ECU and module connectors for green corrosion, bent pins, or plugs that aren't fully clicked home. Wiggle the harness with live data running to catch intermittent dropouts
- 4. Test the earth straps and ground points for the ECU and related modules. A bad earth gives the same symptoms as a broken bus wire
- 5. Get a proper manufacturer-level tool on it to interrogate each module individually and find which one has stopped responding. This is the step that turns guesswork into a real diagnosis
- 6. Check for known software bulletins for your car. Some P0600 cases on later vehicles are fixed with a reflash rather than any hardware
Common questions about P0600
What am I likely to pay to sort this out? +
It swings wildly depending on what's behind it. If it's a battery or a charging fault, you're looking at maybe £100-£200 fitted. A connector clean-up or a wiring repair at an independent garage tends to land somewhere in the low to mid hundreds once they've spent an hour or two tracing it. A full ECU replacement and coding at a main dealer can run into four figures, especially on premium German cars where the module has to be matched to the car. An independent specialist will almost always undercut a franchised dealer on the same job.
How do I work out which of these is actually wrong on my car? +
Start with the battery, because a weak one is the single most likely trigger and it costs nothing to test. If voltage and charging are healthy, the other stored codes are your map. A U0100 alongside the P0600 points at a module that's gone silent on the bus, while a P0700 hints the gearbox module is involved. From there it's connector and earth checks before anyone starts talking about a faulty ECU. A garage with a proper multiplexer tool can ping each module and tell you exactly which one isn't answering.
Is this something I can fix in my own driveway? +
Some of it, yes. Swapping a dud battery, cleaning corroded connectors with contact spray, and checking earth points are all jobs a confident DIYer can manage with basic tools. What you shouldn't do is start back-probing CAN bus wires without knowing the pinout, because the data lines are easy to damage and a slip can take out a control module. The diagnosis side really wants a dealer-grade scanner, so most people end up doing the cheap checks at home and handing the awkward part to a garage.
If I clear the code, will it actually go away? +
If the root cause is still there it'll be back, often within a few drive cycles. Clearing it is only worthwhile after you've fixed something, to confirm the repair held. The exception is a one-off voltage drop, say from a battery that was nearly flat or a jump start that confused the modules. In that case a clear and a few clean starts can settle it for good. If it keeps returning after a reset, you've got a real fault to chase, not a glitch.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →