What does it mean?
P1723 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: TCM A/T Control Relay Line Circuit Malfunction .
Symptoms
- MIL (check engine lamp) on, usually together with the transmission warning lamp
- Transmission falls into limp mode and holds one fixed gear
- Harsh engagement, missing upshifts or no torque converter lockup
- Momentary loss of drive when the relay drops out while moving
- Code returns immediately after clearing if the relay circuit is still open
Likely causes
- Failed A/T control relay with burnt, welded or intermittent internal contacts
- Corroded, loose or backed-out terminals in the relay socket or the TCM connector
- Open circuit or chafed insulation in the relay feed wire running to the solenoid supply
- Short to ground or short to battery on the relay control or output circuit
- Blown fuse, weak power distribution or a poor module ground raising the feed resistance
- Shorted solenoid winding inside the valve body pulling the relay line down
- Internal TCM driver failure, considered only after the relay and wiring test good
How to fix it
- Read the freeze frame and note the system voltage and gear at the moment the code set
- Inspect the relay, its socket and the TCM connector for corrosion, heat marks and spread terminals
- Substitute a known good relay, or bench test the coil and contact resistance
- Measure voltage on the solenoid supply line with the ignition on and again during a road test
- Perform voltage drop tests on the feed and ground legs of the relay circuit
- Measure each solenoid winding at the case connector to rule out a shorted coil loading the line
- Repair the wiring or replace the relay first, and only then consider the TCM