What Does C1861 Mean?
The PRNDL input circuit #4 has experienced a failure, meaning the fourth digital signal from the transmission range sensor is not being received by the control module. This is the last of the binary input lines used to decode gear selector position. The driver may notice gear indicator errors, may be unable to start the vehicle in Park, or the transmission may default to a failsafe operating mode.
Common Causes
35%
Transmission range sensor failure with degraded contacts on the #4 circuit pathway
25%
Open circuit in the PRNDL #4 wiring due to corrosion, abrasion, or a broken wire in the harness
20%
Fluid-contaminated or corroded connector at the transmission range sensor allowing cross-circuit leakage
12%
Shift cable misadjustment or worn cable bushing causing the range sensor to report ambiguous positions
8%
Powertrain or transmission control module internal fault on the #4 input circuit
Diagnostic Steps
1
Monitor all PRNDL input states via the scan tool data stream. Move the gear selector slowly through each position and record which inputs toggle. If input #4 never changes state, the circuit or sensor is at fault.
2
Disconnect and inspect the TRS connector. Look for ATF contamination, green/white corrosion on pins, and any evidence of moisture intrusion. Clean with electrical contact cleaner and dielectric grease.
3
Measure voltage or continuity on the #4 circuit at both the sensor connector and the module connector. Verify the wire is not open (should read less than 2 ohms end-to-end) and is not shorted to adjacent circuits.
4
Verify mechanical alignment of the shift linkage and cable. With the selector in Park, the manual lever on the transmission should be fully seated in the Park detent. Adjust if necessary.
5
If all wiring and sensor tests pass, swap the TRS with a known-good unit (if accessible) or replace the sensor and retest.
Estimated Repair Cost
$150 - $600
Parts + labor, varies by vehicle and location
The PRNDL input circuit #4 has experienced a failure, meaning the fourth digital signal from the transmission range sensor is not being received by the control module. This is the last of the binary input lines used to decode gear selector position. The driver may notice gear indicator errors, may b...
The most common cause of C1861 (PRNDL Input #4 Circuit Failure) is: Transmission range sensor failure with degraded contacts on the #4 circuit pathway
Typical repair costs for C1861 range from $150 to $600, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Failure of PRNDL input #4 can cause the control module to misinterpret the gear selector position. The vehicle may fail to start, may engage an unintended gear, or may lock into limp mode with a single gear available. Do not rely on the gear position indicator until repaired. Drive with caution to a repair shop.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to C1861 to identify the root cause.
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Quick Info
Category
Chassis
System
Transmission / Gear Selection
Difficulty
Type
Manufacturer
Recommended Tools
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