Fault code P1900 – a step-by-step guide to diagnosing and fixing it

Error code P1900 is displayed and the check engine light is on - what does this mean?

The DTC P1900 is a manufacturer-specific fault code that is recognized by the OBD/EOBD diagnostics and indicates a problem with the transmission control module or the communication between the engine and transmission control unit. This trouble code mainly occurs in Ford vehicles and indicates faults in the automatic transmission or the associated electronics.

What causes can this error code have?

• Defective transmission control unit (TCM/PCM)
• Interrupted or damaged cable connections to the transmission
• Faulty CAN bus communication between control units
• Defective transmission sensors or actuators
• Corroded or loose plug connections on the transmission control unit
• Software error in the engine control unit
• Overheating of the transmission electronics
• Voltage problems in the vehicle electrics

What symptoms occur in parallel with fault code P1900?

• Shifting problems: The automatic transmission shifts jerkily or irregularly
• Emergency running program: The transmission switches to safety mode with limited gears
• Starting problems: The engine is difficult to start or stalls while driving
• Loss of power: Reduced engine power and poor acceleration
• Uneven idling: The engine runs unevenly at idle speed
• Transmission warning light: Additional warning lights in the dashboard light up

How can the problem of error code P1900 be rectified?

• The repair requires a systematic diagnosis, as this fault code can have various causes.
• Perform a complete check and reset of all control units with a professional OBD scanner, identify faulty modules and install software updates if necessary
• Check all cable connections between the engine and transmission control unit, repair or replace damaged cables and clean plug connections
• Remove transmission control unit, check for water damage or corrosion and replace with new part or professionally overhauled module if defective
• Completely test the CAN bus system, locate defective bus lines and rectify communication errors between the control units
• Carry out a transmission flush, check all sensors and actuators in the transmission and replace defective components

Completely test the vehicle electrics, identify voltage drops and check earth points and fuses