What Does U0120 Mean?
The powertrain control module has lost communication with the starter/generator control module over the vehicle's communication network (typically CAN bus). This prevents proper coordination between charging system management and engine control functions.
Common Causes
35%
Faulty starter/generator control module with internal processor or communication circuit failure
30%
CAN bus wiring issues including opens, shorts, or high resistance in communication circuit
20%
Corroded or loose electrical connections at starter/generator control module
10%
Power supply issues to starter/generator control module (blown fuse, failed relay)
5%
Powertrain control module internal communication circuit failure
Diagnostic Steps
1
Step 1: Verify all fuses and relays related to starter/generator control module are intact and functioning
2
Step 2: Inspect starter/generator control module connector for corrosion, bent pins, and ensure proper seating
3
Step 3: Check power and ground circuits to starter/generator control module with multimeter
4
Step 4: Use scan tool to monitor CAN bus communication status and check for voltage on CAN high/low circuits (should be approximately 2.5V with key on)
5
Step 5: Test CAN bus termination resistance (should be 60 ohms between CAN high and low with modules disconnected) and check for shorts to power or ground
Estimated Repair Cost
$200 - $1,500
Parts + labor, varies by vehicle and location
The powertrain control module has lost communication with the starter/generator control module over the vehicle's communication network (typically CAN bus). This prevents proper coordination between charging system management and engine control functions.
The most common cause of U0120 (Lost Communication With Starter / Generator Control Module) is: Faulty starter/generator control module with internal processor or communication circuit failure
Typical repair costs for U0120 range from $200 to $1,500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle may experience charging system issues or fail to start. Generally safe to drive short distances if vehicle starts and alternator warning light is not illuminated.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to U0120 to identify the root cause.
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Quick Info
Category
Network
System
Charging System / Communication Network
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
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