E024

ECM Code E024:

VSS Circuit:

DESCRIPTION:

The Vehicle Speed Sensor (VSS) is a permanent magnet pulse generator that is geared to the transmission output to create 4000 voltage pulses/mile. The BCM receives the speed sensor from the VSS, changes the signal to 2000 pulses per mile then sends the 2000 pulse/mile signal to the ECM or CKT 437. The ECM uses VSS input for VCC apply and release determinations, to select between engine speed and throttle angle control of ISC and as a test condition for many codes.

TEST CONDITIONS:

1. Codes E026, E027, E028, E031, E032, and E034 clear.
2. Gear shift in drive or reverse.
3. Not braking (brake switch closed).
4. ISC throttle switch open.
5. MAP less than or equal to 85 KPA.
6. Fourth gear switch open (Trans in fourth gear).
7. Engine speed greater than or equal to 1400 RPM.

FAILURE CONDITIONS:

Vehicle Speed = 0 MPH for 3 seconds.

ACTION TAKEN:

1. ECM illuminates "SERVICE ENGINE SOON" telltale.
2. ECM commands BCM to display "SERVICE SOON" message on CCDIC.
3. Disable VCC.
4. Disable cruise for the entire key cycle.
5. Calculate vehicle speed based on engine speed and gear status.

NOTES ON FAULT TREE:

1. Checking for proper voltage from BCM at connector.

2. Checking for voltage sent from BCM.

3. Before replacing ECM or BCM, remove and replace the BCM "J3" connector and the ECM "J2" connector and ensure that they are latched.

NOTE ON INTERMITTENTS:

Backprobe ECM Pin C8 with a voltmeter to ground. Lift both drive wheels of the vehicle, start engine and allow to idle in drive. Manipulate affected wiring and watch for sudden loss of voltage on ECM Pin C8.

Review the snapshot data parameters stored with this code to verify failure condition. If the failure condition is verified, check and repair intermittent wiring connection, or sensor.