What Does U1021 Mean?
Similar to U1020, this code indicates invalid or missing A/C clutch data on the SCP J1850 network but may represent a different requesting module or circuit. Multiple modules may be unable to receive clutch status information.
Common Causes
30%
Faulty A/C pressure transducer or clutch cycling switch
30%
PCM or body control module communication failure
20%
SCP network bus termination resistor failure
20%
Corroded or loose module connectors affecting network pins
Diagnostic Steps
1
Step 1: Compare U1020 and U1021 freeze frame data to determine which modules are affected
2
Step 2: Check A/C system pressure with gauge set to verify system is operational
3
Step 3: Test A/C clutch operation manually using scan tool active commands
4
Step 4: Measure resistance between SCP bus pins at multiple modules (should be approximately 80-120 ohms)
5
Step 5: Swap suspect modules with known-good units if available to confirm fault location
Estimated Repair Cost
$100 - $850
Parts + labor, varies by vehicle and location
Similar to U1020, this code indicates invalid or missing A/C clutch data on the SCP J1850 network but may represent a different requesting module or circuit. Multiple modules may be unable to receive clutch status information.
The most common cause of U1021 (SCP (J1850) Invalid or Missing Data for Air Conditioning Clutch) is: Faulty A/C pressure transducer or clutch cycling switch
Typical repair costs for U1021 range from $100 to $850, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to drive. A/C may not engage or may cycle improperly, reducing cabin comfort.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to U1021 to identify the root cause.
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Quick Info
Category
Network
System
Network Communication / HVAC
Difficulty
Type
Manufacturer
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