What Does P1820 Mean?
The transfer case clockwise shift relay coil circuit has a general electrical failure, preventing proper energizing of the relay that controls transfer case motor direction. This affects the transfer case's ability to shift between drive modes.
Common Causes
35%
Failed transfer case shift relay with open or shorted coil
30%
Damaged wiring or connector between control module and relay
20%
Transfer case control module driver circuit failure
10%
Blown fuse or fusible link in relay power supply circuit
5%
Poor ground connection at relay or control module
Diagnostic Steps
1
Step 1: Locate transfer case clockwise shift relay and check for power at relay power supply terminal
2
Step 2: Remove relay and test coil resistance (typically 50-120 ohms); replace if open or shorted
3
Step 3: Check for control signal from transfer case module at relay coil control terminal during shift attempt
4
Step 4: Verify ground circuit continuity and quality at relay socket and control module
5
Step 5: If relay and circuits test good, suspect transfer case control module driver circuit failure
Estimated Repair Cost
$120 - $600
Parts + labor, varies by vehicle and location
The transfer case clockwise shift relay coil circuit has a general electrical failure, preventing proper energizing of the relay that controls transfer case motor direction. This affects the transfer case's ability to shift between drive modes.
The most common cause of P1820 (Transmission Transfer Case Clockwise Shift Relay Coil Circuit Failure) is: Failed transfer case shift relay with open or shorted coil
Typical repair costs for P1820 range from $120 to $600, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Transfer case may not shift properly or become stuck in current mode. Could cause driveline damage if operated on dry pavement in 4WD.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1820 to identify the root cause.
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Quick Info
Category
Powertrain
System
Transfer Case Shift Control
Difficulty
Type
Manufacturer
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