P1842 — Transmission Transfer Case Rear Shaft Speed Sensor Circuit Failure

Will P1842 clear itself?

Sometimes P1842 clears after a few drive cycles if the fault was intermittent — for example a loose connector or a tank of bad fuel. The underlying cause usually remains, so the code tends to return. Clear it once; if it comes back, diagnose rather than erase it repeatedly.

How do I diagnose P1842 myself?

Start with a scan: confirm P1842, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the transmission transfer case rear shaft speed sensor circuit, and verify the suspect component against live data before buying parts.

Is it safe to drive with P1842?

Drive only if the transmission still shifts predictably, and avoid highway speeds. Driving with slipping or limp mode accelerates internal wear — every kilometre can add to the final repair bill.

What is the most common cause of P1842?

The most common causes are: low or degraded transmission fluid, wiring or connector faults in the valve body harness, failed shift or pressure control solenoid.

How much does it cost to fix P1842?

Transmission rebuild or replacement — $2,500–$5,500; Replace a shift solenoid — $300–$800; Transmission fluid service — $150–$350; Valve body repair or replacement — $700–$1,500. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

When the engine control module detects a problem in the automatic transmission control system, it stores a specific fault code. P1842 specifically points to a failure in the transmission transfer case rear shaft speed sensor circuit. This code falls within the powertrain category, which covers both engine and transmission-related faults. Essentially, the sensor responsible for monitoring the rear output shaft speed has sent invalid data to the control unit, or the circuit feeding that information has broken down.

The control module sets P1842 after comparing real-time sensor readings against factory-defined acceptable ranges, typically across multiple drive cycles before flagging the fault. When the code is stored, the system also captures a freeze frame snapshot—recording engine RPM, load, coolant temperature, and vehicle speed at the exact moment the failure occurred. Reviewing this snapshot early in the diagnostic process narrows down whether the problem is sensor-related, wiring-related, or caused by internal transmission damage.

Common Symptoms of P1842

• The vehicle may shudder or vibrate noticeably at highway speeds
• In severe cases, the transmission refuses to move the vehicle at all
• The transmission enters limp mode and becomes stuck in a single gear
• Shifting feels harsh, delayed, or erratic
• A Check Engine light or dedicated transmission warning indicator illuminates on the dashboard

What Causes P1842

Several underlying issues can trigger P1842, ranging from simple sensor failures to serious internal damage:

• Internal mechanical wear affecting clutches or the torque converter
• A faulty transmission speed sensor
• Wiring or connector problems within the valve body harness
• A failed shift or pressure control solenoid
• Wear or scoring on the valve body itself
• Low transmission fluid levels or severely degraded fluid

How to Diagnose P1842

Accurate diagnosis prevents unnecessary part replacement and keeps repair costs reasonable:

1. Connect an OBD2 scanner and verify that P1842 is present in the stored codes. Save the freeze frame data immediately—it documents the exact conditions when the fault was recorded and guides the rest of the diagnostic process.
2. Check for any related diagnostic trouble codes alongside P1842, as they often point to the root cause. Research technical service bulletins (TSB) for your specific make and model through the manufacturer's website or nhtsa.gov—many transmission issues have documented factory fixes or software updates.
3. Perform a thorough visual inspection of all wiring and connectors tied to the automatic transmission control system. Look for damaged insulation, corroded pins, chafed wires, or loose connections that could interrupt the sensor signal.
4. Inspect the transmission fluid—check both the level and condition. Dark, burnt-smelling fluid indicates internal component wear and may explain the P1842 trigger.
5. Use a capable scanner to pull transmission-specific codes and monitor live data, including solenoid activation states and input/output shaft speeds.
6. Clear the P1842 code, then drive the vehicle through a complete drive cycle that replicates the conditions captured in the freeze frame. Verify that the code does not return.

Repair Options for P1842

Address the most likely and least expensive causes before committing to major repairs:

• Transmission rebuild or full replacement: $2,500–$5,500
• Replacement of a single shift solenoid: $300–$800
• Complete transmission fluid service: $150–$350
• Valve body repair or replacement: $700–$1,500

The total cost to repair P1842 typically falls between $150 and $5,500, depending on which component is at fault. A proper diagnosis before purchasing parts is essential—the most expensive scenario is rarely the first one to investigate, and fixing minor issues first often resolves the problem at a fraction of the cost.

Can You Drive with P1842?

Exercise caution. Only continue driving if the transmission continues to shift predictably, and avoid highway speeds entirely. Operating the vehicle with slipping gears or while stuck in limp mode accelerates wear on internal components. Every mile driven under these conditions can increase the final repair bill.

Related OBD2 codes

• P1800: Idle Switch Circuit Malfunction
• P1801: Kick Down Switch Circuit Malfunction
• P1802: Neutral Switch Circuit Malfunction
• P1803: Coolant Temperature Circuit Malfunction
• P1804: Hold Switch Circuit Malfunction
• P1805: Transmission Clutch Interlock Safety Switch Circuit Failure