P0790 – Transmission mode selection switch -circuit malfunction

John Kershaw

By John Kershaw (Contact Me)
Last Updated 2016-01-17
Ed.D, PhD Philosophy, BSME

Trouble CodeFault LocationProbable Cause
P0790 Transmission mode selection switch -circuit malfunction Wiring, transmission mode selection switch, ECM/PCM!TCM

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What Does Code P0790 Mean?

DTC P0790 sets when the PCM/TCM has detected a malfunction in the electrical circuit of the transmission mode selector. The switch, system wiring and connectors, and mode actuator are all included in this circuit.

The transmission range (TR) switch or mode selector, also called the manual lever position (MLP) sensor, is used as an input to the PCM/TCM, which indicates the drive range requested by the driver. The transmission range switch is usually located on the outside of the case on the transmission/transaxle housing and attached to the shifter. As the gear range selector is moved, TR switch can make a variety of switch connections for each gear range. These inputs allow the TCM to determine which gear range has been selected. The switch is used by the TCM to

  • Keep the engine from starting in any gear position except park or neutral
  • Allow a progressive 1–2–3–4 shift sequence in drive
  • Limit upshifts in manual ranges
  • Operate the backup lights in reverse

NOTE: Whenever diagnosing a 700 series DTC (Diagnostic Trouble Code) with a transmission, transfer case or other driveline components, check for a DTC under chassis and body systems, not just under “P” or powertrain/engine or emission control type codes. Module communications DTCs are “U” codes. These are most often found when looking for DTCs under chassis or body systems. Chassis related codes are labeled “C” and body system related codes are labeled “B” codes and these can cause drivetrain issues if they affect a sensor that is also used by the heating and air conditioning system.

790

What are the common causes of code P0790 ?

  • Water contamination of the transmission mode switch
  • Open or shorted electrical wiring, damaged, corroded, or disconnected wiring or connectors

What are the symptoms of code P0790 ?

  • MIL (Malfunction Indicator Lamp [Check Engine & Service Engine Soon])lights on with stored historical P0790
  • There may be no distinguishable symptoms
  • Torque converter clutch will not function
  • In some applications, the overdrive light may flash
  • TCM/PCM may also enter “limp-in” mode when this code is stored with harsh shifts

Codes Related to P0790

None

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