What does it mean?
P1601 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Communication Malfunction (between PCM and Throttle Actuator Control Unit) .
Symptoms
- MIL (check engine lamp) on, usually with a reduced power warning
- Engine drops into limp mode with the throttle held close to the idle opening
- Weak or no response to the accelerator pedal, heavy hesitation on acceleration
- Rough idle or stalling when the throttle unit stops receiving commands
- Cruise control unavailable
- Scan tool may fail to communicate with the throttle actuator control unit
Likely causes
- Corroded, loose or backed-out terminals in the throttle actuator control unit connector
- Open circuit, short to ground or chafed insulation on the serial data lines between the two modules
- Low or unstable supply voltage and poor grounds at either module
- Water ingress and corrosion inside the throttle-mounted control unit
- Internal failure of the throttle actuator control unit
- Outdated or corrupted PCM software after a battery or module replacement
- Internal PCM failure, the least likely cause and only after the wiring is proven
How to fix it
- Record freeze frame data and note whether the fault is current or history before clearing anything
- Inspect the throttle unit connector and harness for corrosion, spread terminals and rubbing against the intake or engine mounts
- Measure module supply with the ignition on and perform a voltage-drop test on the ground circuit while cranking
- With both connectors unplugged, test the data lines for continuity, short to ground and short to battery
- Wiggle-test the harness while watching live data to catch an intermittent open circuit
- Confirm the PCM carries the current calibration and that the throttle unit is configured to the vehicle
- Replace the throttle actuator control unit only after wiring and supply checks pass; reprogram or replace the PCM as the final step