What does it mean?
P1694 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: ECM Signal Error .
Symptoms
- MIL on, usually with several other warning lights lit at the same time
- Severe power loss or limp mode with the transmission locked in one gear
- Engine may refuse to start, or start and immediately stall
- Scan tool cannot see the engine module or loses it intermittently
- Instrument cluster gauges reading zero or jumping erratically
- Multiple unrelated codes appearing in other modules at once
Likely causes
- Loss of communication between the engine control module and the module reporting the fault
- Open or shorted wire on the signal line between the two modules
- Corroded, wet or backed-out terminals in either module connector
- Engine control module with no power or ground because of a blown fuse, a failed relay or a bad ground strap
- Calibration mismatch after a module replacement or a reflash
- Internal engine control module failure so it stops broadcasting valid data
- Low system voltage from a failing battery or charging system upsetting the whole network
How to fix it
- Load-test the battery and check charging voltage first; weak supply is the most common trigger for network signal errors
- Scan every module and note which ones report loss of communication with the engine module
- Check the engine module fuses, relays, power feed and grounds directly at its connector
- Inspect the signal and network wiring, especially at the firewall pass-through and along the engine harness
- Measure the signal circuit for continuity, shorts to ground and shorts to power with the modules disconnected
- Verify the module carries the correct current calibration for the vehicle
- Replace and program the engine control module only once supply, grounds and wiring are all proven good