What does it mean?
P1700 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Transmission Control Module (TCM) Requested MIL Illumination .
Symptoms
- MIL on with no obvious engine problem
- Harsh, delayed or completely missing gear changes
- Transmission slipping or flaring between gears
- Limp mode with a single fixed gear and high engine speed on the motorway
- No torque converter lock-up and higher fuel consumption
- Burnt smell from the transmission fluid in advanced cases
Likely causes
- One or more transmission codes stored in the transmission module that trigger the lamp request
- Shift solenoid electrical or hydraulic fault
- Low, burnt or contaminated transmission fluid producing pressure and ratio errors
- Input or output speed sensor signal fault
- Internal transmission wear: slipping clutches, a stuck valve body spool, a failing torque converter clutch
- Transmission module power, ground or communication problem
- Out of date transmission module calibration
How to fix it
- Read the transmission module own codes; the actual fault is stored there, not in the engine module
- Check transmission fluid level, colour and smell on level ground at operating temperature
- Read live data: gear commanded versus gear achieved, input and output speeds, line pressure and fluid temperature
- Diagnose and repair whichever transmission code is actually stored, then clear both modules
- Inspect the transmission case connector and internal harness for fluid intrusion and corrosion
- Check whether an updated transmission calibration exists if the shift complaint matches known behaviour
- Road test after the repair to confirm the lamp request no longer returns