P0959
UniversalP0959 indicates an intermittent electrical issue within the Auto Shift Manual (ASM) mode circuit. This circuit is responsible for controlling the functionality of manual shifting modes in an automatic transmission.
Medium SeverityThis code signifies that the vehicle's computer has detected an inconsistent electrical signal or connection in the Auto Shift Manual (ASM) mode circuit, which controls features like tiptronic or paddle shifters. This intermittent fault can lead to unpredictable or non-functional manual shifting capabilities, affecting the driver's ability to manually select gears.
⚠️ Before You Begin (Safety First)
Always ensure the vehicle is safely parked and the engine is off before attempting any inspection or repair. Disconnect the battery before working on electrical components to prevent accidental short circuits or injury. Be aware that unexpected transmission behavior can pose a safety risk while driving.
Common Symptoms
- Check Engine Light illuminated
- Inability to engage or disengage manual shift mode (e.g., tiptronic, sport mode)
- Manual shift mode functions intermittently or erratically
- Transmission stuck in a specific gear or exhibiting delayed shifts in manual mode
- Vehicle may default to a "limp home" mode
Common Causes
- Loose or corroded electrical connectors in the ASM mode circuit
- Frayed, chafed, or shorted wiring within the ASM mode circuit
- Faulty shift lever assembly or paddle shifter switch
- Intermittent internal fault within the Transmission Control Module (TCM) or Powertrain Control Module (PCM)
- Damaged transmission range sensor or related wiring
Frequently reported on: General/Universal
Diagnostic Steps
- Visually inspect all accessible wiring and connectors related to the transmission and shift lever assembly for signs of damage, corrosion, or looseness.
- Check for any aftermarket installations or modifications that might interfere with the transmission control wiring.
- Use an OBD-II scanner to clear the code and test drive the vehicle to see if the code immediately returns or if the symptoms reappear.
- If accessible and comfortable, gently wiggle wiring harnesses while the engine is running (and safely parked) to try and induce the fault, which can help pinpoint an intermittent connection.
- Consult a vehicle-specific repair manual for precise wiring diagrams and component locations to aid in tracing the ASM mode circuit.
👨🔧 When to Call a Professional
If you lack experience with advanced electrical diagnostics, including the use of multimeters and oscilloscopes to pinpoint intermittent faults, or if the transmission behavior is erratic and unsafe, it is highly recommended to consult a professional automotive technician specializing in transmission and electrical systems.
Commonly Asked Questions
Can I drive with a P0959 code?
While the car may still be drivable, the manual shift mode will likely be inoperative or erratic. It's advisable to get it checked soon, as unexpected transmission behavior can be a safety concern.
Is P0959 a serious code?
It's a medium severity code. While it might not immediately strand you, it affects a core transmission function and could lead to further issues or unsafe driving conditions if left unaddressed.
How expensive is it to fix P0959?
The cost can vary significantly. A simple loose connection might be inexpensive, but if it requires replacing a faulty shift lever assembly, a TCM, or extensive wiring repair, it could range from a few hundred to over a thousand dollars.
What is the "ASM mode circuit"?
ASM stands for Auto Shift Manual. This circuit is an electrical pathway that enables and controls the manual gear selection feature (like paddle shifters or a tiptronic shifter) on an automatic transmission.
Can a low battery cause P0959?
While an extremely low or failing battery can cause various electrical gremlins, it's less likely to specifically cause an intermittent circuit fault within the ASM mode. However, ensuring the battery and charging system are healthy is always a good diagnostic first step.