What Does P1859 Mean?
The TCM has detected an open circuit condition in the transfer case contact plate 'D' circuit. This means there is a complete break in continuity preventing electrical signals from reaching the contact plate.
Common Causes
40%
Broken wire in harness between TCM and transmission/transfer case
30%
Disconnected or loose connector at transmission/transfer case
20%
Failed internal contact plate with broken circuit trace
8%
Corroded connector terminal creating high resistance/open circuit
2%
TCM internal circuit failure
Diagnostic Steps
1
Step 1: Verify connector at transmission/transfer case is fully seated and locked
2
Step 2: Check for bent, backed-out, or corroded pins in transmission connector
3
Step 3: Perform continuity test from TCM connector to transmission connector on contact plate 'D' circuit
4
Step 4: If continuity fails, isolate break location by testing at intermediate connectors or splice points
5
Step 5: Inspect internal contact plate assembly if external wiring shows continuity
Estimated Repair Cost
$100 - $900
Parts + labor, varies by vehicle and location
The TCM has detected an open circuit condition in the transfer case contact plate 'D' circuit. This means there is a complete break in continuity preventing electrical signals from reaching the contact plate.
The most common cause of P1859 (Transmission Transfer Case Contact Plate 'D' Open Circuit) is: Broken wire in harness between TCM and transmission/transfer case
Typical repair costs for P1859 range from $100 to $900, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle may default to 2WD mode or fail to shift properly. Could result in unexpected drivetrain behavior and reduced traction control capability.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1859 to identify the root cause.
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Quick Info
Category
Powertrain
System
Transmission/Transfer Case Control
Difficulty
Type
Manufacturer
Recommended Tools
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