P0600 Code: Serial Communication Link Malfunction
The engine computer lost a dedicated data link to another module, most often the transmission controller.
Unverified: this manufacturer-specific definition comes from a single source or varies by model. Confirm it with a brand-specific scan tool.
At a glance
Severity: Moderate
- Meaning
- Serial Communication Link Malfunction
- System
- ECU & Outputs · Powertrain
- Safe to drive?
- With caution
- Typical repair cost
- $80–$1,900
- DIY difficulty
- Hard
Besides the main CAN network, many powertrains use a dedicated serial link, either between the engine computer (ECM) and the transmission control module, or between two processors inside the ECM itself. P0600 sets when messages on that link go missing, arrive corrupted or come in out of sequence. Exactly which link is monitored differs by manufacturer, so the definition is marked as not fully verified here and the factory wiring diagram for your vehicle decides what to test. In practice, chafed or corroded wiring between the modules, a poor ground and low system voltage are found far more often than a failed controller.
Can I keep driving? Usually drivable at moderate speed, but the transmission may lock into a fixed gear or shift harshly, and some vehicles stall. Avoid highway merges and towing until the link fault is found.
How to read P0600
- P Powertrain
- 0 Generic (SAE)
- 6 Computer & outputs
- 00 Specific fault
Symptoms
- Check engine light, often with a transmission or wrench warning
- Harsh, late or no upshifts; transmission stuck in one gear
- Speedometer, cruise control or tachometer acting up
- Intermittent stalling or hard starting
- Other U-codes stored in the transmission or body modules
- Problem comes and goes over bumps or in wet weather
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Chafed, stretched or corroded wiring on the data link between ECM and transmission module
- Poor module ground or low/unstable system voltage
- Water, ATF wicking or bent pins in the ECM or TCM connector
- Failed transmission control module
- Internal ECM fault on its communication processor
- Software mismatch after one module was replaced or updated
Diagnosis step by step
Scan every module, not just the engine
A full network scan shows who has lost whom. P0600 with U0101 in the ECM points to the transmission side; U-codes in many modules point to a network-wide wiring or power problem.
Tools: OBD-II scanner
Rule out battery and charging problems
Communication faults are very sensitive to voltage dips. Load-test the battery and confirm 13.5–14.8 V with the engine running before you chase wiring.
Tools: Multimeter
Measure the network at the data link connector
With the battery disconnected, resistance between DLC pins 6 and 14 should read about 60 ohms; about 120 ohms means one branch or terminating resistor is open, near zero means a short. With the key on, CAN-high sits around 2.5–3.5 V and CAN-low around 1.5–2.5 V.
Tools: Multimeter
Inspect both module connectors
Many transmission modules sit on or inside the transmission, where ATF can wick up the harness and heat cooks the connector. Look for fluid in the plug, green corrosion and spread terminals at both the ECM and TCM.
Tools: Flashlight, Screwdriver
Wiggle-test the link wiring
Watch live transmission data on the scan tool while flexing the harness along the transmission, firewall and engine mounts. Data that freezes or drops out while you flex pinpoints the damaged section.
Tools: OBD-II scanner
Check software levels before replacing modules
Have the part numbers and calibrations of ECM and TCM compared with the current release. Condemn a module only after wiring, grounds and software are confirmed good, and budget for programming it.
Tools: OBD-II scanner
Where the parts are
- 1Battery
- 2Alternator
- 3Engine computer (ECM)
- 4CAN bus
- 5Transmission
- 6Wheel speed sensor
- 7High-voltage battery
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Repair data link wiring or connector | No | $120–$450 |
| Clean and repair module grounds | No | $80–$250 |
| ECM or TCM software update | No | $100–$250 |
| Replace transmission control module with programming | No | $500–$1,500 |
| Replace ECM with programming | No | $700–$1,900 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Emissions / smog test impact
Will fail
P0600 turns on the check engine light, so the vehicle fails an OBD emissions or smog test. After the repair and a code clear, drive several days so the readiness monitors can complete.
Frequently asked questions
Why does my transmission shift hard with P0600?
The transmission computer relies on torque and throttle data from the engine computer. When that link fails it falls back to a protective default, often firm shifts or a single gear, until the data returns.
Is P0600 the same as U0101?
They're related but not identical. U0101 means a module lost contact with the transmission controller over the network, while P0600 is the engine computer reporting a fault on its own serial link. Seeing both together narrows the search to the ECM–TCM connection.
Can a transmission fluid leak cause P0600?
Yes, indirectly. On vehicles with the TCM on the transmission, fluid can seep into the connector or travel up the harness by capillary action and corrode the data pins. Fix the leak and clean the connector, or the fault will return.
Will clearing the code fix it?
Only if it was a one-time glitch, for example after a jump start. If the code returns, the link has a real wiring, power or module problem that needs to be traced.
Sources
- SAE J2012 – Diagnostic Trouble Code Definitions
- ISO 15031-6 – Road vehicles, diagnostic trouble code definitions (EOBD)
- Manufacturer public service information (cross-checked)
- Methodology: How We Build Code Pages · Data Sources We Use · Editorial Policy