P0979 — Shift Solenoid “C” Control Circuit Low #

Note: The code description may vary depending on the vehicle manufacturer.

• P0979: Transmission Shift Solenoid “C” Control Circuit Low (Generic OBD-II)
• P0979: Shift Solenoid “C” Electrical Circuit Low (Honda/Acura)
• P0979: Solenoid Valve “C” Control Circuit Low (Ford/Lincoln)
• P0979: Shift Solenoid “C” Malfunction (Toyota/Lexus)

Code P0979 Summary #

P0979 is a generic OBD-II trouble code indicating a low voltage condition in the control circuit for shift solenoid “C” within the transmission. The shift solenoids are electronic valves that regulate hydraulic fluid flow, enabling smooth gear changes. When the control module (PCM/TCM: Powertrain or Transmission Control Module) detects electrical resistance or voltage below a specified threshold, it sets this code. This issue can lead to erratic shifting, harsh engagement, or even limp mode operation. Although not immediately catastrophic, ignoring P0979 can result in further transmission damage over time.

Common Symptoms for Code P0979 #

Drivers may notice a variety of symptoms when the P0979 code is present. These can range from minor annoyances to significant drivability issues, depending on the severity and how long the problem has been present.

• Delayed or harsh shifting between gears
• Transmission stuck in a single gear (“limp” mode)
• Check Engine Light (CEL) or Malfunction Indicator Lamp (MIL) illuminated
• Poor acceleration or decreased fuel efficiency
• Unusual noises during shifting (clunks, bangs)
• Transmission overheating in some cases

Likely Causes for Code P0979 #

The most common causes for a P0979 code relate to electrical and mechanical faults in the shift solenoid “C” circuit. Here’s what typically triggers the code, listed in order of frequency:

1. Faulty shift solenoid “C” (internal electrical failure or sticking valve)
2. Wiring issues (damaged, chafed, corroded, or disconnected wires/connectors in the solenoid circuit)
3. Faulty transmission control module (TCM) or powertrain control module (PCM)
4. Low transmission fluid level or contaminated fluid (rarely, but can contribute to solenoid malfunction)
5. Electrical short to ground in the solenoid control circuit

Step-by-Step Diagnostics for Code P0979 #

A thorough, methodical approach is key to pinpointing the root cause of P0979. Here’s a structured process any technician or advanced DIYer can follow:

• Step 1: Verify the code and clear it. Road test the vehicle to see if P0979 returns.
• Step 2: Check transmission fluid level and condition; top up or replace if necessary.
• Step 3: Inspect the wiring harness and connectors at the transmission for signs of corrosion, damage, or loose connections.
• Step 4: Using a digital multimeter, test the shift solenoid “C” circuit for continuity and proper voltage.
• Step 5: If accessible, measure resistance at the solenoid itself and compare with OEM specifications.
• Step 6: If wiring and solenoid test good, use a scan tool to monitor live data and check TCM/PCM outputs.
• Step 7: If all else checks out, suspect a faulty TCM/PCM (rare). Consult OEM diagnostic flowcharts before replacement.

Possible Repairs for Code P0979 #

Depending on what the diagnosis uncovers, several repair actions may resolve P0979. Always address the root cause rather than simply clearing the code.

• Replace shift solenoid “C” if it is shorted, open, or stuck
• Repair or replace damaged wiring/connectors in the solenoid circuit
• Top up or flush transmission fluid if contaminated or low
• Replace TCM/PCM only if confirmed faulty (after all other checks)
• Clean or secure electrical grounds as needed

Is It Safe to Drive with Code P0979? #

Limited — Use caution. While some vehicles may continue to drive with minimal symptoms, P0979 can lead to harsh or unpredictable shifting and may trigger limp mode, restricting transmission operation to a single gear. Continuing to drive for an extended period risks further transmission damage. If the vehicle is shifting erratically or stuck in gear, it’s best to avoid driving until repairs are completed.

Vehicles Most Commonly Affected by Code P0979 #

While P0979 can appear on nearly any modern vehicle equipped with electronically controlled automatic transmissions, certain manufacturers and models see this code more frequently due to design and component similarities.

• Honda/Acura (Accord, Civic, CR-V, Odyssey)
• Ford/Lincoln (Fusion, Escape, Focus)
• Toyota/Lexus (Camry, Corolla, RAV4)
• Chrysler/Dodge/Jeep (Grand Caravan, Journey)
• Nissan/Infiniti (Altima, Sentra, Rogue)

Common Mistakes & Best Practices for Code P0979 #

Misdiagnosis or incomplete repairs are common with P0979. Here’s how to avoid the usual pitfalls and ensure a lasting fix:

• Don’t replace the solenoid without checking wiring and fluid first.
• Avoid clearing the code before fully diagnosing the root cause.
• Always use OEM or high-quality replacement parts.
• Verify all repairs with a scan tool and a test drive.
• Document any findings and parts replaced for future reference.

Express FAQ for Code P0979 #

Here are quick answers to the most common questions about P0979:

• Can a bad battery or alternator cause P0979?
  Unlikely. This code is almost always related to the transmission solenoid circuit, not general vehicle power supply issues.
• Will a transmission flush fix P0979?
  Only if the problem is caused by dirty or low fluid. Most cases involve electrical faults in the solenoid or wiring.
• Is P0979 the same as a slipping transmission?
  Not exactly. While both can affect shifting, P0979 specifically points to an electrical issue with shift solenoid “C”, not mechanical slipping of clutches or bands.