P1842 Transfer Case Rear Speed Sensor Circuit
The P1842 code indicates a fault in the transfer case rear shaft speed sensor circuit. This sensor monitors the rotation speed of the rear output shaft and sends a variable frequency signal to the transmission control module (TCM) or powertrain control module (PCM). The code sets when the signal is out of range, erratic, or when a discrepancy is detected between this sensor and other vehicle speed sensors. This code is specific to Ford vehicles with four-wheel drive or all-wheel drive systems that use a transfer case.
01. Most Common Causes
- Faulty or worn transfer case rear shaft speed sensor
- Damaged, corroded, or loose wiring in the sensor circuit
- Short circuit or open circuit in the sensor harness to the TCM/PCM
- Internal transfer case mechanical wear (e.g., damaged reluctor ring)
- Sensor connector issues due to water intrusion or contamination
- Faulty TCM or PCM (less common)
02. Symptoms You Will Notice
- Check Engine Light or 4WD warning light illuminated
- Erratic or inoperative speedometer
- Harsh or delayed transmission shifting
- Loss of 4WD or AWD functionality
- Reduced fuel economy
03. Step-by-Step Diagnosis
Scan for codes and record freeze frame data
Visually inspect the sensor and wiring for damage, corrosion, or loose connections
Test sensor resistance and signal output with a multimeter or oscilloscope
Compare sensor readings with other speed sensors using a scan tool
Check for mechanical issues in the transfer case, such as a damaged reluctor ring
If all else is normal, test the TCM/PCM for proper signal processing
1. Frequently Asked Questions
Is it safe to drive?▼
You can drive short distances, but the vehicle may experience shifting issues or loss of 4WD. It's best to diagnose and repair promptly to avoid further damage.
How much does it cost to fix?▼
Repair costs typically range from $150 to $400, depending on whether the sensor alone needs replacement or if wiring repairs or transfer case work is required.