P1847

What Does Code P1847 Mean?

DTC P1847 signifies an “Open Circuit” within the Transmission Transfer Case Contact Plate ‘A’ system. This code specifically indicates that the Powertrain Control Module (PCM) or Transfer Case Control Module (TCCM), depending on the vehicle architecture, is not detecting the expected electrical continuity or signal from the transfer case contact plate designated as ‘A’. The contact plate system is an integral part of the transfer case’s mode selection and position feedback mechanism. It typically consists of a series of conductive tracks and brushes or pins that provide variable resistance or discrete switched signals to the control module, indicating the current position or desired mode of the transfer case (e.g., 2WD, 4HI, 4LO, N). An open circuit implies a complete break in this electrical path, preventing the control module from accurately determining the transfer case’s state or from receiving necessary feedback for proper operation. This usually means the control module measures infinite resistance or an unexpected voltage state on the specific circuit associated with contact plate ‘A’, triggering the diagnostic trouble code.

Common Symptoms

• Malfunction Indicator Lamp (MIL) or “Service Engine Soon” illumination.
• 4WD/AWD indicator lamp may illuminate, flash, or display an error message.
• Inability to engage or disengage 4WD/AWD modes (e.g., stuck in 2WD, inability to shift into 4HI or 4LO).
• Transfer case may remain in a default mode, potentially causing reduced traction in certain conditions or binding on dry pavement.
• Abnormal noises from the transfer case during attempted mode changes.
• Transfer case shift switch or selector may not respond or function intermittently.
• Reduced vehicle performance or erratic behavior in varying terrain if the 4WD system cannot be properly controlled.

What Causes the Code P1847?

• Damaged or corroded wiring harness leading to the transfer case contact plate/switch assembly.
• Loose or corroded electrical connectors at the transfer case, transfer case shift motor, or control module.
• Faulty transfer case contact plate assembly due to worn contacts, internal circuit board damage, or contamination.
• Faulty transfer case shift motor/actuator assembly where the contact plate is often integrated.
• Water intrusion into the transfer case shift motor or connector housing, leading to corrosion and open circuits.
• Mechanical damage to the transfer case or shift mechanism that has physically severed or dislodged the contact plate components.
• PCM/TCCM failure (less common, but possible, particularly if multiple related codes are present).

How to Diagnose and Troubleshoot

Diagnosis of P1847 requires a methodical approach, utilizing a digital multimeter (DMM) and a capable OBD-II scanner with bidirectional control. Begin by connecting an OBD-II scanner to verify P1847 is present and check for any related transfer case or communication codes. Perform a visual inspection of the transfer case area, focusing on the shift motor, wiring harness, and connectors for obvious signs of damage, corrosion, or looseness.

1. Retrieve Freeze Frame Data: Note conditions under which the code was set (engine RPM, vehicle speed, transfer case mode, etc.) to aid in reproduction and diagnosis.

2. Inspect Wiring and Connectors: Carefully examine the electrical harness from the transfer case shift motor/sensor assembly back to the PCM/TCCM. Look for chafed, pinched, or broken wires. Disconnect and inspect all relevant connectors for bent pins, corrosion, or contamination. Pay particular attention to the main connector at the transfer case and the module connector.

3. Transfer Case Contact Plate Resistance Test:

• Locate the electrical connector for the transfer case shift motor/sensor assembly. Disconnect it.
• Identify the pins corresponding to the contact plate ‘A’ circuit as per the vehicle-specific wiring diagram.
• Using a DMM set to ohms, measure the resistance across the relevant pins on the transfer case side of the connector. An open circuit will typically register as infinite resistance (OL or ‘1’ on most DMMs), confirming an internal break within the transfer case component. Compare this reading against manufacturer specifications, if available.
• If an open circuit is confirmed here, the issue is likely internal to the transfer case shift motor/contact plate assembly.

4. Wiring Harness Continuity Test:

• If the contact plate assembly shows good continuity (or expected resistance) when tested directly, then proceed to test the wiring harness.
• With the transfer case connector and the PCM/TCCM connector (if accessible and safe to disconnect) both disconnected, use the DMM to check for continuity between the corresponding pins of the contact plate ‘A’ circuit at both ends of the harness. An open circuit here indicates a break in the wiring itself.
• Also, check for shorts to ground and shorts to voltage within the harness by testing resistance between each wire of the contact plate ‘A’ circuit and a known good chassis ground, and then against a fused 12V source, respectively.

5. Voltage Supply and Ground Test: Verify that the transfer case shift motor/sensor assembly is receiving proper power and ground signals from the control module when commanded (if applicable to the specific circuit design). Use the DMM to measure voltage at the connector terminals with the ignition on and the transfer case commanded into different modes using a bidirectional scan tool.

6. Bidirectional Control (if applicable): Use a scan tool to command the transfer case shift motor to cycle through its positions. Monitor live data for the contact plate ‘A’ signal. If the signal remains static or indicates an open circuit despite motor actuation, it further points to a faulty contact plate or its wiring.

Recommended Repairs and Solutions

Once the source of the “open circuit” is precisely identified, the following repairs are typically recommended:

• Repair or Replace Damaged Wiring: If the diagnostic steps indicate a break or severe damage within the wiring harness, perform precise solder repairs or replace the affected section of the harness. Ensure connections are properly sealed to prevent future moisture intrusion.
• Clean or Replace Corroded Connectors: If corrosion is found at the connector terminals, carefully clean them using an electrical contact cleaner and a small brush. If corrosion is extensive or pins are damaged, replace the entire connector housing and terminals.
• Replace the Transfer Case Shift Motor/Actuator Assembly: In many modern applications, the contact plate ‘A’ is an integral, non-serviceable part of the transfer case shift motor assembly. If the internal contact plate is confirmed faulty, replacing the entire shift motor assembly is often the most practical and reliable solution.
• Replace Transfer Case Contact Plate Assembly: For older or specific vehicle models where the contact plate is a separately serviceable component, replacement of just the contact plate assembly may be possible.
• Address Water Intrusion: If water ingress was the root cause, identify the entry point and seal it appropriately after completing repairs. This might involve replacing damaged rubber boots or gaskets.
• Clear DTCs and Test Drive: After performing repairs, clear the P1847 code and any related codes from the control module’s memory. Conduct an extensive test drive, cycling through all transfer case modes multiple times, to ensure the repair is effective and the code does not return.