P0956
UniversalAutomatic Shift Manual (ASM) Mode Circuit Range/Performance
Medium SeverityThis code indicates an issue within the circuit that controls the Automatic Shift Manual (ASM) mode of your vehicle's transmission. This problem can prevent the transmission from shifting correctly when attempting to use manual gear selection or may cause the gear display to show incorrect information.
⚠️ Before You Begin (Safety First)
Driving with transmission issues can be dangerous and potentially lead to further damage. If your vehicle exhibits erratic shifting, is stuck in a gear, or becomes difficult to control, pull over safely as soon as possible. Always disconnect the battery before performing any electrical diagnostics or repairs to prevent electrical shock or damage to vehicle components.
Common Symptoms
- Check Engine Light illuminated
- Inability to select or engage manual shift mode (e.g., paddle shifters, tiptronic)
- Transmission stuck in a single gear (limp mode)
- Erratic or harsh shifting in automatic mode
- Incorrect gear displayed on the dashboard
- Vehicle not responding to paddle shifter inputs
Common Causes
- Faulty wiring or connectors in the ASM mode circuit (e.g., open, short, high resistance)
- Defective ASM mode switch or sensor (e.g., within the shifter assembly or paddle shifters)
- Issues with the Transmission Control Module (TCM) or Powertrain Control Module (PCM)
- Internal transmission mechanical issues (less common for this specific code, but possible if affecting circuit performance)
- Low transmission fluid level or contaminated fluid (indirectly impacting sensor readings)
Frequently reported on: General/Universal
Diagnostic Steps
- Visually inspect all wiring harnesses and connectors associated with the shifter assembly, transmission, and any paddle shifters for signs of damage, corrosion, or looseness.
- Check for any technical service bulletins (TSBs) or recalls related to P0956 for your specific vehicle make and model.
- Using a digital multimeter, test the continuity and resistance of the ASM mode circuit wires according to your vehicle's service manual specifications.
- If accessible and testable without specialized equipment, check the function of the ASM mode switch or sensor for proper operation.
- Ensure transmission fluid levels are correct and the fluid is not heavily contaminated. While not a direct fix for an electrical circuit issue, it can sometimes influence sensor performance.
- Clear the code with an OBD-II scanner and perform a test drive to see if the code returns.
👨🔧 When to Call a Professional
If you lack experience with advanced electrical diagnostics, have specialized transmission tools, or are uncomfortable working with complex vehicle systems, it is highly recommended to consult a professional mechanic or transmission specialist immediately. Incorrect diagnosis or repair can lead to more costly transmission damage.
Commonly Asked Questions
Can I continue driving with a P0956 code?
It is not advisable to drive for extended periods with a P0956 code. Transmission problems can quickly worsen, potentially leading to a complete transmission failure or creating unsafe driving conditions due to unpredictable shifting.
What does 'ASM Mode' refer to?
ASM Mode, or Automatic Shift Manual Mode, is a feature in automatic transmissions that provides the driver with the ability to manually select gears, typically using paddle shifters on the steering wheel or a dedicated gate on the shifter lever.
Is a P0956 repair something a DIY mechanic can handle?
Diagnosing and repairing a P0956 code can be challenging for a DIY mechanic. It often involves intricate electrical diagnostics of complex circuits and potentially transmission components, which may require specialized tools, diagrams, and advanced knowledge.
Will simply clearing the P0956 code fix the problem?
Clearing the code with an OBD-II scanner will only turn off the check engine light temporarily. The code will reappear if the underlying electrical or mechanical issue causing the P0956 code has not been properly identified and repaired.
Could a low battery or bad alternator cause this code?
While a severely low battery or a malfunctioning charging system can lead to various electrical issues and sometimes trigger false codes, it's generally unlikely to be the direct cause of a P0956. However, it's always good practice to ensure your battery and charging system are in good health.