DTC Troubleshooting: P0851 (K20C1) - Honda Civic FC/FK 2016-2021

1.

Problem verification:

Problem verification

?1.	Turn the vehicle to the ON mode.

?2.	Clear the DTC with the HDS.

?3.

Check for Pending or Confirmed DTCs with the HDS.

DTC Description	Confirmed DTC	Pending DTC
P0851 Neutral Position Sensor A Circuit Low Voltage

Is DTC P0851 indicated?


	YES

The failure is duplicated. Go to step 2.


	NO

Intermittent failure, the system is OK at this time. Check for poor connections or loose terminals at the neutral position sensor and the PCM. If the on-board snapshot of this DTC is recorded, try to reproduce the failure under the same conditions with the on-board snapshot.?

2.

DTC check:

DTC check

?1.

Check for Pending or Confirmed DTCs with the HDS.

DTC Description	Confirmed DTC	Pending DTC
P0851 Neutral Position Sensor A Circuit Low Voltage
P1707 Neutral Position Sensor B Circuit Low Voltage

Are DTC P0851 and P1707 indicated at the same time?


	YES

Go to step 3.


	NO

Go to step 5.

3.

Determine possible failure area (neutral position sensor, others):

Determine possible failure area (neutral position sensor, others)

?1.	Turn the vehicle to the OFF (LOCK) mode.

?2.

Disconnect the following connector.

Neutral position sensor 4P connector

?3.	Turn the vehicle to the ON mode.

?4.

Measure the voltage between test points 1 and 2.

Test condition	Vehicle ON mode
	Neutral position sensor 4P connector: disconnected
Test point 1	Neutral position sensor 4P connector (female terminals) No. 1:
Test point 2	Body ground

Is there about 5.0 V?


	YES

Replace the neutral position sensor.?


	NO

Go to step 4.

4.

Open wire check (VCC1 NSS line):

Open wire check (VCC1 NSS line)

?1.	Turn the vehicle to the OFF (LOCK) mode.

?2.	Jump the SCS line with the HDS, and wait more than 1 minute.

?3.

Disconnect the following connector.

PCM connector No. 1 (96P)

?4.

Check for continuity between test points 1 and 2.

Test condition	Vehicle OFF (LOCK) mode
	Neutral position sensor 4P connector: disconnected
	PCM connector No. 1 (96P): disconnected
Test point 1	Neutral position sensor 4P connector (female terminals) No. 1:
Test point 2	PCM connector No. 1 (96P) No. 62

Is there continuity?


	YES

The VCC1 NSS wire is OK. Check for any authorized service information related to the DTCs or symptoms you are troubleshooting, or substitute a known-good PCM, then recheck. If DTC P0851 goes away and the PCM was substituted, replace the original PCM.?


	NO

Repair an open in the VCC1 NSS wire between PCM connector No. 1 terminal No. 62 and the neutral position sensor.?

5.

Determine possible failure area (neutral position sensor, others):

Determine possible failure area (neutral position sensor, others)

?1.	Turn the vehicle to the OFF (LOCK) mode.

?2.

Disconnect the following connector.

Neutral position sensor 4P connector

?3.

Connect terminals A and B with a jumper wire.

Terminal A	Neutral position sensor 4P connector (female terminals) No. 1:
Terminal B	Neutral position sensor 4P connector (female terminals) No. 3:

?4.	Turn the vehicle to the ON mode.

?5.

Check the parameter(s) below with the HDS.

Signal	Current conditions
Signal	Values	Unit
NEUTRAL POSITION SENSOR 1

Is about 5 V indicated?


	YES

Replace the neutral position sensor.?


	NO

Go to step 6.

6.

Open wire check (NSS1 line):

Open wire check (NSS1 line)

?1.	Turn the vehicle to the OFF (LOCK) mode.

?2.	Jump the SCS line with the HDS, and wait more than 1 minute.

?3.

Disconnect the following connector.

PCM connector No. 1 (96P)

?4.

Check for continuity between test points 1 and 2.

Test condition	Vehicle OFF (LOCK) mode
	Neutral position sensor 4P connector: disconnected
	PCM connector No. 1 (96P): disconnected
Test point 1	Neutral position sensor 4P connector (female terminals) No. 3:
Test point 2	PCM connector No. 1 (96P) No. 30

Is there continuity?


	YES

The NSS1 wire is not open. Go to step 7.


	NO

Repair an open in the NSS1 wire between PCM connector No. 1 terminal No. 30 and the neutral position sensor.?

7.

Shorted wire check (NSS1 wire):

Shorted wire check (NSS1 wire)

?1.

Check for continuity between test points 1 and 2.

Test condition	Vehicle OFF (LOCK) mode
	Neutral position sensor 4P connector: disconnected
	PCM connector No. 1 (96P): disconnected
Test point 1	Neutral position sensor 4P connector (female terminals) No. 3:
Test point 2	Body ground

Is there continuity?


	YES

Repair a short in the NSS1 wire between PCM connector No. 1 terminal No. 30 and the neutral position sensor.?


	NO

The NSS1 wire is OK. Check for any authorized service information related to the DTCs or symptoms you are troubleshooting, or substitute a known-good PCM, then recheck. If DTC P0851 goes away and the PCM was substituted, replace the original PCM.?