Serial Communication Link
What it means
The engine computer (ECU) has detected a problem exchanging data over the serial communication link with another control module, such as the transmission module (TCM), or between processors inside the computer itself. The most common cause is a power supply problem or faulty wiring and connectors, and sometimes an internal module fault.
Symptoms4
- Check engine light on, sometimes with communication codes in other modules.
- Harsh shifting or the transmission going into limp mode.
- Reduced performance or intermittent hesitation while driving.
- Hard starting or stalling in a few cases.
Possible causes6
- Weak battery or low supply voltage while running.
- Corroded or loose connectors at the engine computer or the other module.
- Damaged communication wiring or poor ground connections.
- Water or moisture inside connectors.
- A fault in the other control module on the link.
- Internal engine computer failure (less common).
How to diagnose6
- Read codes from all modules; communication codes in several modules point to wiring or power supply.
- Test the battery and charging system and confirm the voltage stays stable while running.
- Check the supply fuses and ground points for the engine computer and connected modules.
- Disconnect and inspect the connectors for corrosion or loose pins.
- Check continuity of the communication wires against the manufacturer wiring diagram.
- Look for service bulletins or software updates for this code at the dealer.
How to fix6
- Charge or replace the battery if it is weak.
- Clean and tighten the connectors and ground points.
- Repair any broken or shorted wire.
- Update the engine computer or other module software if an update exists.
- Replace and program the module proven to be faulty.
- Clear the codes, then road test and confirm the code does not return.
Repair cost
In Saudi riyals; the highlighted part is the expected range for this fault.
The cost is low for a connector, ground or battery fix, and rises when a control module must be replaced and programmed.
Prices are rough estimates for common cars at independent workshops and vary with the car and the source of the part.
Prices last updated: September 2026
Frequently asked questions
Does this code mean the engine computer is bad?
Not necessarily. Most cases come from a power, ground or corroded connector problem, and the computer should only be condemned after those are checked.
Why do transmission problems show up with it?
The engine computer shares data with the transmission module. When that data is lost, the transmission module may enter limp mode, causing harsh or limited shifting.
This guide is for information only and does not replace an inspection by a qualified technician. If the fault involves brakes, steering, engine temperature, electrics or refrigerant, do not attempt the repair yourself.
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