What does it mean?
P1596 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Automatic Transaxle Diagnosis Input Signal Circuit High Input .
Symptoms
- Check engine light on, usually with a transmission warning lamp or message
- Harsh, delayed or flaring gear changes
- Transmission drops into limp mode and holds a single fixed gear
- Torque converter lock-up does not engage, so engine speed stays high at cruising speed
- Higher fuel consumption and increased transmission temperature
- Kickdown does not respond when the pedal is pressed
Likely causes
- Signal wire shorted to battery voltage where the harness has chafed
- Open circuit on the signal line, which lets the module input sit high
- Corroded or unlatched connector at either the transmission control unit or the engine control module
- Poor ground on the transmission control unit, raising the level of its output signal
- Water intrusion into the transmission connector, common where it passes through the case seal
- Internal fault in the transmission control unit output stage
- Damaged input circuit inside the engine control module
How to fix it
- Read the transmission control unit codes as well as the engine codes, since the source is usually on the transmission side
- Check the transmission control unit supply voltage and grounds, and clean any corroded ground points
- Inspect both module connectors and the transmission case connector for water, oil and corroded terminals
- Measure the voltage on the diagnostic signal line with the ignition on and again with the engine running
- Disconnect the transmission control unit and see whether the reading changes, isolating the module from the wiring
- Test the line for continuity between modules and for a short to battery voltage
- Repair the wiring first, and replace the transmission control unit only after the circuit has been proven good