P0790: A fault in the electrical circuit of the transmission's normal/performance mode switch
Normal/performance switch circuit malfunction
Severity: Severity not verified — if the car runs badly, have it inspected
The sources define the code and list symptoms from none to harsh shifts in limp mode, but give no severity rating.
It gets more serious if:
- Inspect soon: Inspect soon if the transmission shifts harshly or the overdrive light flashes, since TroubleCodes.net says the computer may enter limp mode.
P0790 in short
P0790 means the transmission computer has found a fault in the circuit of the normal/performance mode switch. Water in the switch or damaged, corroded or disconnected wiring are the listed causes. Some cars show no symptoms; others lose torque converter lockup or shift harshly in limp mode. Have it checked if shifting changes.
The mode switch lets the driver choose between normal and performance shift patterns. The engine or transmission computer watches the circuit and sets P0790 when the signal is not what it expects.
TroubleCodes.net lists water in the switch and open, shorted, corroded or disconnected wiring as the causes. The code may cause no noticeable symptoms, or the torque converter clutch may stop working.
Most likely causes
These are general causes for this code across vehicles. None is specific to one make or model.
Cause 1: Water in the mode switch
Common general cause- Why it ranks here
- TroubleCodes.net lists water contamination of the switch first.
- What would change this
- Rises if the switch or its connector is wet or corroded. Falls if it is clean and dry.
Cause 2: Open, shorted, corroded or loose wiring or connector
Common general cause- Why it ranks here
- Listed with the switch as a cause of a circuit fault, and a circuit code points at the wiring as readily as the part.
- What would change this
- Rises if a continuity or short check finds a fault. Falls if the wiring tests good.
What to test first
Start at step 1. Each result tells you what it means and where to go next.
Step 1: Look at the mode switch and its connector for water, corrosion, bent pins or a loose fit.
IfWater, corrosion or damage is visible
It meansThe switch or connector is the likely cause.
IfEverything looks clean
It meansWiring needs a meter test.
Step 2: Check the switch circuit wiring for opens and shorts with a multimeter, following the wiring diagram for the vehicle.
Warning:Probing connectors with the ignition on can short a pin and damage the transmission computer. Disconnect the battery or use back-probes as the service manual directs.
IfOpen or short found
It meansRepair the wiring or connector.
Points to: Open, shorted, corroded or loose wiring or connector
IfWiring tests good
It meansSuspect the switch itself or the computer; a shop should confirm.
Symptoms
- Check engine light with possibly no change in how the car drives
- Torque converter clutch not locking up
- Overdrive light flashing on some vehicles Gets more serious: stop and have it checked.
- Harsh shifts if the computer enters limp mode Gets more serious: stop and have it checked.
How to fix
Parts and cost context
- Transmission control module (TCM):The transmission computer monitors the circuit, but the switch and wiring are listed as likely causes first. Labour varies; get a quote.
Labor varies by vehicle and shop; get a quote before you approve a repair.
Compare used part prices on PartPriceGuideOn your vehicle
We don't have reviewed vehicle-specific evidence for P0790 yet. The causes and tests above apply across vehicles.
Related codes
No curated relationships for P0790 yet.
P0790 questions
Is it safe to drive with P0790?
Sometimes there are no symptoms, but harsh shifts or a flashing overdrive light suggest limp mode, so get it checked soon.
Sources and review
- Last reviewed
- Written by
- Saurabh K.
- Editorial review
- Pending
- Technician review
- Technician review pending
This page explains what a code usually means; it is not a substitute for a professional inspection. How we source and review · Report an error