Engine-Codes - Generic - P0851

P0851 - Park/Neutral Position Switch Circuit Low Voltage

Repair Importance Level: 3/3
Repair Difficulty Level: 2/3  What is this?
Table of contents

P0851 Possible Causes

  • Faulty Park/Neutral Switch
  • Park/Neutral Switch harness is open or shorted
  • Park/Neutral Switch circuit poor electrical connection

How is the P0851 code repair?

Start by checking the "Possible Causes" listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector's pins.

What is the cost to diagnose the P0851 code

Labor: 1.0

The cost to diagnose the P0851 code is 1.0 hour of labor. The auto repair labor rates vary widely across the country, and even within the same city. Most auto repairs shops charge between $75 and $150 per hour.
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Possible Symptoms

  • Engine Light ON (or Service Engine Soon Warning Light)

P0851 Meaning

The transmission manual shift shaft switch assembly, also known as the Internal Mode Switch (IMS), is a sliding contact switch attached to the manual shift shaft inside the transmission case. The Park/Neutral Position (PNP) Switch is integrated into the IMS and connects to the Transmission Control Module (TCM) lead-frame through a short wire harness. The 5 inputs to the TCM from the transmission manual shift shaft switch assembly indicate the transmission gear selector lever position. This information is used for engine start enable, engine controls as well as determining the transmission shift patterns. The state of each input is available for display on the scan tool. The five input parameters represented are Signal A, Signal B, Signal C, Signal P (Parity), and Signal N (Park/Neutral Start Signal). Park/Neutral Signal is sent from the Park/Neutral switch directly to the Engine Control Module (ECM) and is used for engine start enable. The Park/Neutral Signal circuit is not connected to the TCM internally; the circuit uses the TCM as a pass-through connector only. The ECM Park/Neutral diagnostic monitors the Park/Neutral Signal circuit to detect Low voltage when the ECM expects to see High voltage and High voltage when the ECM expects to see Low voltage.

More Information

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Information for specific makes

  • P0851 BUICK Park/Neutral Position Switch Circuit Low Voltage
  • P0851 CADILLAC Park/Neutral Position Switch Circuit Low Voltage
  • P0851 CHEVROLET Park/Neutral Position Switch Circuit Low Voltage
  • P0851 CHRYSLER Park/Neutral Position Switch Circuit Low Voltage
  • P0851 DODGE Park/Neutral Position Switch Circuit Low Voltage
  • P0851 GMC Park/Neutral Position Switch Circuit Low Voltage
  • P0851 JEEP Park/Neutral Position Switch Circuit Low Voltage
  • P0851 PONTIAC Park/Neutral Position Switch Circuit Low Voltage
  • P0851 SATURN Park/Neutral Position Switch Circuit Low Voltage
  • P0851 SUBARU Park/Neutral Position Switch Circuit Low Voltage

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