Vehicle Systems Interfaces

The engine management system interfaces with the transmission control module, the instrument pack and the air conditioning compressor clutch circuit to provide operational control, sensor input and data input.

TRANSMISSION CONTROL MODULE INTERFACE

Engine Torque Reduction
The ECM receives two ignition timing retard inputs from the TCM: transmission shift "up/down" signal (IGNITION SELECT) (pulsed signal), and transmission "shift in progress" signal (IGNITION RETARD) (pulsed signal). Refer to Ignition Timing, for a detailed explanation.

Engine Speed And Load
The ECM outputs engine load and speed signals (PULSED SIGNALS) to the TCM. The TCM uses the engine load and speed data to determine shift patterns and torque converter clutch apply and release.

Engine Idle Speed
The transmission decoder module (XJ6), rotary switch (XJS) outputs gear position signals to the ECM. When the gear selector is in R, D, 2 or 3, the signal is 5 volts; when the gear selector is in P or N, the signal is ground or 0 volts. The ECM uses the gear position inputs to control idle speed and for DTC 59. Refer to Ignition Timing and Idle Speed Control for a detailed explanation.

INSTRUMENT PACK INTERFACE

Vehicle Road Speed
The instrument pack outputs a road speed signal (pulsed signal) to the ECM. The ECM uses the signal to determine idle speed control functions.

Low Fuel Level (1992 MV ON [ECM part no. DBC 9622 ON])
The instrument pack outputs a fuel level voltage signal to the ECM. When the voltage drops below 5.7 volts, 11 liters (2.5 gallons) fuel remaining, fuel metering diagnostics (OBD) are canceled. Cancelling the fuel metering diagnostics prevents the ECM from flagging DTCs caused by the vehicle running out of fuel.

Engine Speed
Engine speed is output to the instrument pack for operation of the tachometer. Engine speed is sensed from the ignition coil primary circuit (1990 - 92 MY Sedan and XJS). The ECM outputs an engine speed signal (pulsed signal) to the instrument pack (1993 MY ON Sedan).

Fuel Metering Pulse
The ECM outputs a fuel metering pulse to the instrument pack for use by the trip computer (average fuel consumption, instantaneous fuel consumption).

Fuel Fail Warning
If the OBD system detects a fault, the ECM outputs a fuel fail warning signal (ground) to the instrument pack.

Air Conditioning Compressor Clutch Interface
When the air conditioning compressor clutch is operating, a parallel circuit applies battery voltage to the ECM. The ECM uses this signal to determine the need for idle speed control compensation.