What Does P1904 Mean?
The transmission control module has detected an open circuit in the ground return path for the transfer case contact plate. This prevents proper electrical communication with the transfer case position sensors and mode selection system.
Common Causes
40%
Corroded or broken ground wire connection at transfer case
30%
Damaged transfer case contact plate or electrical connector
20%
Loose or corroded ground bolt/stud mounting point
7%
Internal transfer case wiring harness damage
3%
Transmission control module ground circuit fault
Diagnostic Steps
1
Step 1: Locate transfer case ground wire connections and inspect for corrosion, looseness, or physical damage
2
Step 2: Clean and tighten all ground connections, ensuring good metal-to-metal contact
3
Step 3: Test continuity from transfer case contact plate ground terminal to chassis ground and TCM ground
4
Step 4: Inspect transfer case electrical connector and contact plate for damage, corrosion, or broken traces
5
Step 5: If ground circuit tests good, inspect internal transfer case wiring or replace contact plate assembly
Estimated Repair Cost
$100 - $500
Parts + labor, varies by vehicle and location
The transmission control module has detected an open circuit in the ground return path for the transfer case contact plate. This prevents proper electrical communication with the transfer case position sensors and mode selection system.
The most common cause of P1904 (Transmission Transfer Case Contact Plate Ground Return Open Circuit) is: Corroded or broken ground wire connection at transfer case
Typical repair costs for P1904 range from $100 to $500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Transfer case mode selection may be unreliable or non-functional. Vehicle can typically be driven in the current transfer case mode but changing modes may not be possible until repaired.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1904 to identify the root cause.
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Quick Info
Category
Powertrain
System
Transfer Case Electrical System
Difficulty
Type
Manufacturer
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