What Does P0979 Mean?
The TCM has detected that the Shift Solenoid C (SS-C) control circuit voltage is below the expected threshold, indicating a short to ground condition. The solenoid circuit is being held low against TCM commands, locking SS-C in one state. This prevents the transmission from properly engaging or disengaging the gears controlled by SS-C, typically affecting third gear, fourth gear, or overdrive engagement.
Safety Warning
The transmission may be unable to achieve certain gears, stuck in one gear, or in limp mode. This limits vehicle performance and can create safety issues if the vehicle cannot maintain highway speeds. Minimize driving and seek repair immediately.
Common Causes
35%
Short to ground in the SS-C internal transmission wiring harness
30%
Shift Solenoid C coil internally shorted to ground
20%
Corroded or contaminated terminals at the transmission case connector causing a ground path
10%
External harness chafed or pinched against a ground source
5%
TCM internal SS-C driver failed in the low state
Diagnostic Steps
1
Disconnect the transmission case connector and measure SS-C solenoid resistance — a reading well below specification confirms an internally shorted solenoid.
2
With the connector disconnected, check insulation resistance from each SS-C wire to the transmission case (ground) — should be over 10K ohms. Low values identify a harness short to ground.
3
Inspect the case connector for fluid contamination, corroded pins, and any evidence of pin-to-case or pin-to-pin shorts. Clean and dry all contacts.
4
Examine the external harness for chafed insulation or pinch points, particularly near brackets, sharp edges, or hot exhaust components.
5
If all harness and solenoid tests are within specification, measure voltage at the TCM SS-C output to determine if the TCM driver is internally faulted.
Estimated Repair Cost
$200 - $1,400
Parts + labor, varies by vehicle and location
The TCM has detected that the Shift Solenoid C (SS-C) control circuit voltage is below the expected threshold, indicating a short to ground condition. The solenoid circuit is being held low against TCM commands, locking SS-C in one state. This prevents the transmission from properly engaging or dise...
The most common cause of P0979 (Shift Solenoid "C" Control Circuit Low) is: Short to ground in the SS-C internal transmission wiring harness
Typical repair costs for P0979 range from $200 to $1,400, depending on the vehicle, location, and whether you do it yourself or go to a shop.
The transmission may be unable to achieve certain gears, stuck in one gear, or in limp mode. This limits vehicle performance and can create safety issues if the vehicle cannot maintain highway speeds. Minimize driving and seek repair immediately.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0979 to identify the root cause.
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Quick Info
Category
Powertrain
System
Automatic Transmission / Transaxle
Difficulty
Type
Generic (SAE)
Recommended Tools
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