What does it mean?
P1672 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: A/T (TCM) FI Data Line Circuit Malfunction .
Symptoms
- MIL on with a transmission warning lamp that may come and go
- Harsh, delayed or hunting shifts
- Transmission drops into failsafe intermittently and recovers after a restart
- Torque converter lock-up cycling in and out at steady speed
- Fuel economy drops noticeably, and the fault often appears only on rough roads or over bumps
Likely causes
- High resistance or an intermittent open in the data wire between the two modules
- Corroded, loose or backed-out pins at either module connector
- Wire chafed and shorting intermittently to ground or to a neighbouring circuit
- Poor shared ground between the transmission and engine modules
- Low or unstable battery voltage, especially during cranking
- Internal communication fault in the TCM or in the engine control module
- Wiring damaged during accessory installation or bodywork
How to fix it
- Check battery voltage, terminal condition and charging output before anything else
- Read live data from both modules and note the moment communication drops out
- Unplug and inspect both connectors, checking terminal tension and looking for corrosion and fretting on the pins
- Measure the data line resistance end to end and test for shorts to ground and to battery voltage
- Voltage-drop test the ground points shared by the two modules
- Move the harness section by section while watching the scan tool for dropouts, focusing on grommets and tie-down points
- Repair the damaged wiring first; module replacement and programming is the last step