What does it mean?
P1671 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: A/T (TCM) FI Data Line No Signal .
Symptoms
- MIL on with a transmission warning lamp
- Transmission locked in a single failsafe gear: very high engine speed at road speed, or a sluggish take-off
- Torque converter lock-up never engages
- Harsh or completely missing shifts
- Gear position display blank or wrong, and the scan tool cannot communicate with the TCM at all
Likely causes
- TCM unpowered: blown fuse, failed relay or a bad ground at the module
- Data line between the TCM and the engine module open, or shorted to ground
- Corroded or water-damaged TCM connector, often located under a kick panel or floor trim
- Internal failure of the TCM
- Harness damage from a previous repair, accessory installation or rodent chewing
- Low battery voltage or a poor battery terminal connection
- TCM replaced without the required programming
How to fix it
- Try to communicate with the TCM; a total no-response points at power, ground or a shorted data line rather than at intermittent data
- Check the TCM fuses and relay, then measure supply voltage and ground at the module connector under load
- Unplug the TCM connector and inspect it for water, corrosion and pushed-out pins
- Check the data line for continuity to the engine module and test it for a short to ground
- Wiggle-test the harness in the kick panel and floor area while watching the scan tool for communication
- Verify battery condition and charging voltage before condemning any module
- Repair the harness, then replace and program the TCM only if supply and wiring are proven good