What does it mean?
P1660 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: A/T (TCM) FI Data Line Circuit Malfunction .
Symptoms
- MIL on, usually with a transmission warning lamp
- Transmission locked in a failsafe gear, or harsh and delayed shifts
- Torque converter lock-up does not engage, so engine speed stays high on the highway
- Noticeable increase in fuel consumption
- Intermittent or no communication with the TCM on a scan tool
Likely causes
- Open, shorted or high-resistance data wire between the TCM and the engine control module
- Corroded or backed-out terminals at either module connector
- Poor common ground shared by the two modules
- Water intrusion at a kick panel, floor or bulkhead connector
- Low or unstable battery voltage causing communication dropouts
- Internal communication failure of the TCM or the engine module
- Aftermarket wiring spliced into the data line during an accessory installation
How to fix it
- Check battery voltage, terminal condition and charging output first, since low voltage alone produces communication faults
- Unplug and inspect the TCM and engine module connectors for corrosion, moisture and pushed-out pins
- Measure the data line end to end for continuity and test it for shorts to ground and to battery voltage
- Voltage-drop test the ground points shared by both modules
- Back-probe the data line while moving the harness in the kick panel and floor area to reveal an intermittent break
- Repair the damaged wiring, clear the codes and road test through a full shift range
- Replace and program a module only after the harness and grounds are proven good