TEST CONDITIONS: Codes EO26, EO27, EO28, EO31, EO32, and EO34 clear. Transmission in reverse or drive, and brake switch closed (not braking). ISC throttle switch open. MAP less than or equal to 85 kPa (Kilopascals). Transmission in 4th gear (4th gear switch open). Engine speed greater than or equal to 1400 RPM.

FAILURE CONDITIONS: Vehicle speed equals zero MPH for 3 seconds.

ACTION: ECM turns on "ENGINE CONTROL SYSTEM" light. ECM commands BCM to display "SERVICE SOON" on CCDIC panel. Viscous Converter Clutch (VCC) and cruise control disabled. Use vehicle speed information coming from BCM serial data.

The Vehicle Speed Sensor (VSS) is a permanent magnet pulse generator that is geared to transmission output to create 4000 voltage pulses per mile. The BCM receives speed sensor signal from VSS, changes signal to 2000 pulses per mile, then sends the 2000 pulse signal to the ECM over circuit No. 437.

The ECM uses VSS input for VCC apply and release determinations, to select between RPM and throttle angle control of ISC, and as a test condition for many codes.

NOTE: Test numbers refer to test numbers on diagnostic chart.

Checks for proper voltage from BCM at ECM connector.
This step checks for voltage sent from BCM.
Before replacing ECM or BCM, unplug and plug in connectors to ensure that they are latched properly.

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

ECM Code EO24 - Speed Sensor Circuit Problem: Notes

Use the Manual With the Right Hardware

When to See a Mechanic