Description

Neutral/Drive Switch Description

1. Fault Codes:
High Load Neutral/Drive Fault P1514
Gear Change Neutral/Drive Fault P1516
Cranking Neutral/Drive Fault P1517

2. Monitoring Procedure

Summary
Problems with the neutral/drive switch will be detected using a number of tests. Two tests check whether the neutral/drive switch is incorrectly indicating neutral, by detecting high load conditions or gear changes. A single test checks for whether the neutral/drive switch is incorrectly indicating drive, by detecting cranking. If these tests are not passed then the appropriate fault count will be incremented. If the count reaches a given threshold then a fault is present. While a fault is present a default value for the neutral/drive switch will be supplied to the rest of the system.

Cranking Test
The drive position test will test for engine conditions that indicate that the gearbox is in neutral yet the switch reads drive. The drive position test involves monitoring whether CRANKING mode has been entered. Upon entry to CRANKING mode then a delay of a minimum period of NEUT DRV DIAG CRK INIT DELAY should occur to allow the systems voltages to recover from any start-up transients. Sample the neutral/drive switch during the remaining cranking period. The sampling technique is required to avoid the effects of electrical noise during CRANKING. Any switch samples that read drive while CRANKING are fault events. If a greater proportion of samples than NEUT DRV DIAG CRK PERCENT MIN indicate drive then there is a fault present. Once cranking mode is entered, wait for NEUT DRV DIAG CRK INIT DELAY. As long as the engine is still cranking then start sampling, recording both the total number of samples and the number of those switch samples that were fault events, i.e. switch reads drive. Only stop sampling once the engine stops cranking or the total number of samples is NEUT DRV DIAG CRK SAMPLES MAX. As long as at least a minimum of NEUT DRV DIAG CRK SAMPLES MIN samples have occurred before the end of the cranking period, then continue the test.

The proportion of samples that indicate drive will be calculated; if NEUT DRV DIAG CRK PERCENT MIN indicates drive then it indicates that the switch is in drive so there is a fault present.

Neutral Position Test

I. High Load Test.
This test establishes that there is a false indication of neutral from the neutral / drive switch while the gearbox is in drive by checking for high engine load whenever high engine speed is seen in neutral. High load indicates that the vehicle is in gear, and low load implies neutral.

The test operates as follows:
1. While in neutral, if the engine load exceeds the NEUT_DRV_HIGH_LOAD_THRESH when the engine speed exceeds EUT_DRV_DIAG_ENGINE_SPD_MIN, then the fault counter is incremented. If the counter reaches NEUT_DRV_DIAG_HIGH_LOAD_FAULT_LIMIT then a fault is recorded.
2. While in neutral, if the engine load is less than or equal to the NEUT_DRV_DIAG_HIGH_LOAD_THRESH when the engine speed still exceeds NEUT_DRV_DIAG_ENGINE_SPD_MIN, then decrement the fault counter.
3. If the neutral/drive switch equals drive, then the fault counter is decremented down to a limit of zero.

II. Gear Change Test
The test involves monitoring for gear change requests while the switch indicates neutral. This can be done by monitoring for ignition alteration due to the presence of the GEAR_CHANGE_IN_PROGRESS flag, which occurs during gear changes. If a gear change request occurs while the neutral /drive switch indicates neutral, then the gear change fault event counter will be incremented. If a gear change request occurs while the neutral drive switch indicates drive, then decrement the gear change fault event counter. If the counter reaches NEUT_DRV_DIAG_GEAR_FAULT _LIMIT then a fault is recorded.

3. Primary Detection Parameter
Neutral drive switch input - an internal state generated from the volts output of the neutral drive switch.

4. Fault Criteria Limits

High Load Test - false indication of neutral from the neutral drive switch while the gearbox is in drive.

Cranking Test - Indication from engine conditions that the gearbox is in neutral yet the switch reads drive.

Gear Change Test - indication from a gear change in progress flag that a gear change is in progress when the neutral/drive switch indicates that the gearbox is in neutral.

5. Monitoring Conditions

Cranking Test - The engine status is cranking.
NEUT_DRV_DIAG_CRK_INIT_DELAY, used to ensure that the system's voltages is stable, 1.0sec
NEUT_DRV_DIAG_CRK _SAMPLES_MAX, maximum number of samples taken to verify switch functionality, 50
NEUT_DRV_DIAG_CRK_SAMP_MIN, minimum number of samples taken to verify switch functionality,15
NEUT_DRV_DIAG_CRK_PERCENT_MIN, minimum percentage of drive indications from samples taken required to indicate a fault, 90

High Load Test - The engine load must be equal to or below 80% and the engine speed must be equal to or above 1500RPM. Water temperature above 80�C. the gearbox does not indicate a fault.

Gear Change Test - The gearbox does not indicate a fault, the engine is not in stall.

6. Monitoring Time Length / Frequency of Checks
The frequency of the Neutral/Drive diagnostic is 10Hz.

7. Criteria for Storing Fault Code
Two successive journeys where the Neutral/Drive diagnostic indicates a failed neutral/drive switch.

8. Criteria for Illuminating MIL
The MIL will not be illuminated.

9. Criteria for Determining Out of Range Input Signals
The neutral/drive switch produces a non-linear output; the criteria will be signal/no signal.