P1794-Speed Sensor Ground Error: Notes

Fig 1: Speed Sensor Circuit Diagram

Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.

For a complete wiring diagram  , refer to appropriate SYSTEM WIRING DIAGRAMS article.

Theory of Operation 

The transmission system uses two speed sensors, one to measure input RPM and one to measure output RPM. These inputs are essential for proper transmission operation. Therefore, the integrity of this data is verified through the following checks: 

1. When in gear, if the gear ratio does not compare to a known gear ratio, the corresponding in-gear trouble code is set (DTCs P0731.36). 
2. An excessive change in input or output speeds indicating signal intermittent which may result in the DTCs P0715 and/or P0720 to set. 
3. If the common speed sensor ground circuit is lost, both sensor inputs will read the signal from the input speed sensor at idle in neutral. Since the input speed sensor reads 60 teeth from the input clutch hub and the output speed sensor reads 30 teeth from the park gear, the result is an apparent speed ratio of 1:2 and may cause the DTC P1794 to set when at a stop. 
   • When Monitored: 

     The gear ratio is monitored continuously while the Transmission is in gear. 

   • Set Condition: 

     After a controller reset in neutral and a ratio of input to output, of 1 to 2. This DTC can take up to five minutes of problem identification before illuminating the MIL. 

Always perform the 45RFE/545RFE PRE-DIAGNOSTIC TROUBLESHOOTING PROCEDURE before proceeding.