What does it mean?
P1857 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Load Signal Error Message From Engine Control .
Symptoms
- Check engine lamp on, usually with engine-side codes stored as well
- Shift points wrong: shifting too early, too late or hunting between gears
- Harsh or soft shifts that do not match throttle input
- No kick down when the accelerator is pressed hard
- Limp mode, single-gear operation and reduced drivability
Likely causes
- Engine-side fault such as a mass air flow or manifold pressure sensor problem making the load value invalid
- Communication bus wiring damaged: a broken, shorted or corroded data line between the modules
- Corroded or backed-out terminals at a module connector interrupting the message
- Low system voltage or a weak battery causing modules to drop messages
- Ground fault at one of the control modules
- Software or calibration mismatch after a module replacement or update
- Failed engine control module output
How to fix it
- Scan every module, not just the transmission, and write down all stored codes
- Diagnose and repair engine load sensor faults before touching the transmission
- Compare the engine load value reported by the engine module with the one the transmission module receives
- Check battery voltage and charging system, since low voltage upsets module communication
- Inspect the data bus wiring and module connectors for corrosion, chafe and loose terminals
- Measure the bus circuits for resistance and shorts if communication faults are also stored
- Verify both modules carry the correct current calibration, and clear codes to confirm the message is restored