Antitheft and Alarm Systems

DTC 15 Vehicle Speed Signal Voltage Low:

DTC 15 Vehicle Speed Signal Voltage Low (Part 1 Of 2):

DTC 15 Vehicle Speed Signal Voltage Low (Part 2 Of 2):

CIRCUIT DESCRIPTION
The Theft Deterrent Module (Immobilizer) uses terminal 7 to send the vehicle speed signal and the frequency code (imo signal) to terminal 79 of the Engine Control Module (ECM).

After the ECM requests the imo signal, the Theft Deterrent Module internally blocks the speed signal and sends the imo signal after the ECM requests the imo signal. Both signals cannot be transmitted at the same time. The ECM compares the received imo signal with the programmed stored signal.

If both codes are the same, the engine control functions (fuel pump drive and injector signals) are released. Non matching codes block the engine functions and the car cannot be started.

CONDITIONS FOR SETTING THE DTC
1. DTC 15 indicates a short to ground or an open in the speed/imo signal circuit.
2. The above conditions must be fulfilled for at least 0.51 seconds.

ACTION TAKEN WHEN THE DTC SETS
The engine starts then stalls.

CONDITIONS FOR CLEARING THE DTC
^ The conditions for the fault are no longer present.
^ The ignition switch was cycled 20 times.
^ The use of the scan tool.

DIAGNOSTIC AIDS
^ Using a DMM, check the ground circuit at terminal 4. Typical voltage drop readings are 100mV or less. When measuring the resistance it should measure at close to 0 (zero) ohms.
^ Use Terminal Repair kit J 38125-A or J 3561-A to gauge all terminal contacts.
^ Check for damaged connectors and poor wire to terminal connections. Refer to General Troubleshooting Procedures for procedure.
^ If the DTC is an intermittent DTC, try performing the tests shown while "wiggling" wiring and connectors, this can often cause the malfunction to appear.

TEST DESCRIPTION
The following numbers refer to the step numbers on the diagnostic table:
2. This checks if the Theft Deterrent Module transmits the immobilizer signal.
3. Include turning the key to the On position when checking for a short to B+.
12. The module may be faulty if no trouble is found in the power circuits, if no trouble is found in the ground circuits, or if no trouble if found in the connection at the Theft Deterrent Module. However, this is an extremely unlikely failure.