P0953
UniversalAutomated Manual Transmission (ASM) Control Circuit High
High SeverityThis code indicates that the vehicle's powertrain control module (PCM) has detected a higher-than-normal voltage reading in the Automated Manual Transmission (ASM) control circuit. This typically means the ASM system, which automates gear shifts and clutch operation in a manual transmission, may not function correctly, leading to shifting problems or the inability to select gears.
⚠️ Before You Begin (Safety First)
Always disconnect the battery before performing any electrical work on your vehicle to prevent short circuits or injury. Be cautious of hot engine components and moving parts when working near the transmission. Use appropriate jack stands if lifting the vehicle.
Common Symptoms
- Check Engine Light illuminated
- Transmission stuck in gear or limp mode
- Harsh or erratic shifting
- Inability to shift gears
- Vehicle may not move
- Unusual noises from the transmission
Common Causes
- Open circuit or short to voltage in the ASM control circuit wiring
- Faulty Automated Manual Transmission (ASM) control module
- Corroded, loose, or damaged electrical connectors for the ASM system
- Faulty transmission range sensor (less common, but possible if integrated)
- Problem with the Powertrain Control Module (PCM) - rare
Frequently reported on: Smart Fortwo 2008-2015, Alfa Romeo Selespeed systems, BMW models with SMG transmission, Mercedes-Benz Sprinter (some automated manual configurations)
Diagnostic Steps
- Safely lift and support the vehicle to gain access to the transmission and ASM components.
- Visually inspect all wiring harnesses and connectors leading to the ASM control module and transmission for any signs of damage, fraying, corrosion, or loose connections.
- Using a digital multimeter, test the relevant wires in the ASM control circuit for excessive voltage (short to voltage) or an open circuit, following your vehicle's specific wiring diagram.
- Inspect the ground connections for the ASM module and ensure they are clean and securely fastened.
- If a specific wiring fault (open or short) is identified, repair or replace the damaged section of the harness.
- Clear the fault code with an OBD-II scanner and perform a test drive to confirm the repair.
👨🔧 When to Call a Professional
Diagnosing a 'control circuit high' condition often requires advanced electrical troubleshooting skills, including the use of a multimeter and access to detailed wiring diagrams specific to your vehicle. If you lack these tools or experience, it is strongly recommended to seek professional automotive technician assistance to prevent further damage.
Commonly Asked Questions
What does 'ASM' stand for in P0953?
ASM stands for Automated Manual Transmission. It is a type of manual transmission that uses electronics and actuators to automatically shift gears and operate the clutch, eliminating the need for a clutch pedal.
Can I continue driving my car with a P0953 code?
It is not recommended to drive with a P0953 code. This code indicates a significant issue with your transmission's control system, which can lead to unpredictable shifting, being stuck in gear, or a complete loss of drive, posing a serious safety risk.
Is a P0953 repair usually expensive?
The cost varies greatly. A simple wiring repair might be inexpensive. However, if the ASM control module itself is faulty, replacement can be very costly due to the price of the specialized module and the complex programming often required.
How do I test the ASM control circuit for a 'high' condition?
Testing typically involves using a digital multimeter to check for abnormal voltage readings (higher than expected) or open circuits within the relevant wiring and connectors, always referencing your vehicle's specific wiring diagrams and diagnostic procedures.
Is P0953 related to a standard automatic transmission problem?
No, a P0953 code specifically refers to an Automated Manual Transmission (ASM), which is mechanically distinct from a traditional automatic transmission that uses a torque converter. The diagnostic approach for each is different.