With Manual Transmission

COMMUNICATION PROBLEMS WITH SCAN TOOL

MFI = LH 3.2 Multiport Fuel Injection System.
DI = EZK 129 Distributor Ignition System.

Fault Sources:
^ Communication is established only with MFI system and engine starts:
- DI system diagnostic lead.
- Scan Tool (ST) wiring.

- Proceed to: Checking DI System Diagnostic Lead, section below.

^ Communication is established only with DI system and engine starts:
- MFI system diagnostic lead.
- ST wiring.

- Proceed to: Checking MFI System Diagnostic Lead, section below.

^ No communication established and engine starts:
- ST wiring.

- Proceed to: Checking ST Diagnostic Leads, section below.

^ Contact established with MFI system only and engine fails to start:
- DI system busbar 30 supply.
- DI system busbar 15 supply.

- Proceed to: Checking DI System Busbar 30 Supply, section below.

^ Communication established with DI system only and engine fails to start:
- Supply from MFI system main relay.
- MFI system busbar 15 supply.
- MFI system signal ground.
- Control signal to MFI system main relay.

- Proceed to: Checking MFI System Busbar 15 Supply, section below.

^ No communication established and engine tails to start:
- Lead between battery and ICM / MFI #10.
- Ground lead between engine and battery.
- Ignition switch.
- Lead between ignition switch and ICM / MFI terminal A30.

- Proceed to: Checking DI / MFI Busbar 30 Supply, section below.

NOTE: Connect battery charger or extra battery if communication problem occurs only when starting engine.

TESTING PROCEDURE





Checking DI System Diagnostic Lead
^ Switch ON ignition.
^ Connect voltmeter between DLC terminal 6 and ground.

Instrument should indicate over 5 Volts.

If reading is correct:
- Check ST diagnostic lead for damage.
If reading is incorrect:
- Proceed to: Checking Resistance of DI System Diagnostic Lead to Ground.





Checking Resistance of DI System Diagnostic Lead to Ground
^ Switch OFF ignition.
^ Wait 30 seconds.
^ Connect ohmmeter between DI DLC terminal 6 and ground.

If resistance is infinite:
- Check lead between ICM B5 and DLC terminal 6 for open-circuit.
If resistance is approx. 0 Ohms:
- Check lead between ICM B5 and DLC terminal 6 for short-circuit to ground.





Checking MFI System Diagnostic Lead
^ Switch ON ignition.
^ Connect voltmeter between DLC terminal 2 and ground.

Instrument should indicate over 5 Volts.

If reading is correct:
- Check ST diagnostic lead for damage.
If reading is incorrect:
- Proceed to: Checking Resistance of MFI Diagnostic Lead to Ground.





Checking Resistance of MFI System Diagnostic Lead to Ground
^ Switch OFF ignition.
^ Wait 30 seconds.
^ Connect ohmmeter between DLC terminal 2 and ground.

If resistance is infinite:
- Check lead between MFI B5 and DLC terminal 2 for open-circuit.
If resistance is approx. 0 Ohms:
- Check lead between MFI B5 and DLC terminal 2 for short-circuit to ground.





Checking ST Diagnostic Leads
^ START engine.
^ Attempt to establish communication with ST.

If communication is not established:
- STOP engine and START again.
- Attempt to establish communication with ST.
If communication is still not established:
- Switch ST OFF and ON again.
- Attempt to establish communication with ST.
If communication is still not established:
- Check ST diagnostic leads for damage.





Checking DI System Busbar 30 Supply
^ Connect test box to DI system and check ground terminals.
^ Plug ICM into test box adapter.
^ Switch ON ignition.
^ Connect voltmeter across #10 (ICM A10) and #20 (ICM A20) on test box.

Instrument should indicate battery voltage.

If reading is correct:
- Proceed to: Checking DI System Busbar 15 Supply.
If reading is incorrect:
- Check lead between ICM A1O and battery positive terminal for open-circuit.





Checking DI System Busbar 15 Supply
^ Switch ON ignition.
^ Connect voltmeter across #30 (ICM A30) and #20 (ICM A20) on test box.

Instrument should indicate battery voltage.

If reading is correct:
- Check all signals to and from the ICM.
- See: COMPUTERS AND CONTROL SYSTEMS / TESTING AND INSPECTION / DIAGNOSTIC CHARTS / NON-TROUBLE CODE CHARTS / ECM PINOUT & TERMINAL I.D. CHARTS / IGNITION SYSTEM.
If reading is incorrect:
- Check lead between ICM A30 and fuse No. 1, terminal 2, for open-circuit.





Checking MFI System Busbar 15 Supply
^ Connect test box to MFI system and check ground terminals.
^ Plug MFI module into test box adapter.
^ Switch ON ignition.
^ Connect voltmeter across #30 (MFI A30) and #20 (MFI A20) on test box.

Instrument should indicate battery voltage.

If reading is correct:
- Proceed to: Checking Supply From Main Relay to MFI Module.
If reading is incorrect:
- Check lead between MFI A30 and fuse No. 1, terminal 2, for open-circuit.





Checking Supply From Main Relay to MFI Module
^ Switch ON ignition.
^ Connect voltmeter across #19 (MFI A19) and #20 (MFI A20) on test box.

Instrument should indicate battery voltage.

If reading is correct:
- Check all signals to and from MFI module.
- See: COMPUTERS AND CONTROL SYSTEMS / TESTING AND INSPECTION / DIAGNOSTIC CHARTS / NON-TROUBLE CODE CHARTS / ECM PINOUT & TERMINAL I.D. CHARTS / FUEL INJECTION SYSTEM.
If reading is incorrect:
- Proceed to: Checking Supply to Main Relay, Terminal 4.





Checking Supply to Main Relay, Terminal 4
^ Switch OFF ignition.
^ Disconnect main relay (2/32) connector.
^ Connect voltmeter between main relay connector terminal 4 and ground.

Instrument should indicate battery voltage.

If reading is correct:
- Proceed to: Checking Supply to Main Relay, Terminal 2.
If reading is incorrect:
- Check lead between main relay connector terminal 4 and battery positive terminal for open-circuit.





Checking Supply to Main Relay, Terminal 2
^ Switch OFF ignition.
^ Remove main relay.
^ Connect voltmeter between main relay connector terminal 2 and ground.

Instrument should indicate battery voltage.

If reading is correct:
- Proceed to: Checking Control Signal to Main Relay.
If reading is Incorrect:
- Check lead between main relay connector terminal 2 and battery positive terminal for open-circuit.





Checking Control Signal to Main Relay
^ Switch ON ignition.
^ Remove main relay.
^ Connect voltmeter between main relay connector terminal 1 and battery positive terminal.

Instrument should indicate battery voltage.

If reading is correct:
- Proceed to: Checking Voltage From Main Relay.
If reading is incorrect:
- Check lead between MFI A24 and main relay connector terminal 1 for open-circuit.





Checking Voltage From Main Relay
^ Switch ON ignition.
^ Connect main relay to connector.

Relay should click when connected.

If click is heard:
- Check lead between MFI A19 and main relay connector terminal 3 for open-circuit.
If click is not heard:
- Proceed to: Checking Signal Lead.





Checking Signal Lead
^ Switch OFF ignition.
^ Disconnect main relay from connector.
^ Connect ohmmeter between main relay connector terminal 3 and ground.

If resistance is approx. 0 ohms:
- Check lead between MFI A19 and main relay connector terminal 3 for short-circuit to ground.

NOTE: This lead is also connected to:

- Terminal 1 on each injector.
- HO2S heater terminal 1.
- IAC valve terminal 2.
- MAF sensor terminal 3.
- EGR controller terminal 2.

^ Install new main relay when fault has been corrected.

If resistance is over approx. 0 ohms:
- Try with new main relay.





Checking Busbar 30 Supply to DI / MFI Systems
^ Connect test box to DI system and check ground terminals.
^ Plug ICM into test box adapter.
^ Switch ON ignition.
^ Connect voltmeter across #10 (ICM A10) and #20 (ICM A20) on test box.

Instrument should indicate battery voltage.

If reading is correct:
- Proceed to: Checking Busbar 15 Supply to DI / MFI Systems.
If reading is incorrect:
- Check lead between ICM A1O and battery positive terminal for open-circuit.





Checking Busbar 15 Supply to DI / MFI Systems
^ Switch ON ignition.
^ Connect voltmeter between #30 (ICM A30) and #20 (ICM A20) on test box.

Instrument should indicate battery voltage.

If reading is correct:
- Check all signals to and from MFI module and ICM.
- See: COMPUTERS AND CONTROL SYSTEMS / TESTING AND INSPECTION / DIAGNOSTIC CHARTS / NON-TROUBLE CODE CHARTS / ECM PINOUT & TERMINAL I.D. CHARTS.
If reading is incorrect:
- Proceed to: Checking Fuse No. 1.





Checking Fuse No. 1
^ Check that fuse No. 1 is intact.

If fuse is intact:
- Proceed to: Checking Busbar 15 Supply to Fuse.
If fuse is faulty:
- Check lead between ICM A30 and fuse No. 1, terminal 2, for short-circuit to ground.





Checking Busbar 15 Supply to Fuse
^ Switch ON ignition.
^ Remove fuse.
^ Connect voltmeter between rear terminal of No.1 fuse holder and ground.

Instrument should indicate battery voltage.

If reading is correct:
- Check lead between ICM A30 and fuse No. 1, terminal 2, for open-circuit.
If reading is incorrect:
- Proceed to: Checking Busbar 15 Supply From Ignition Switch.





Checking Busbar 15 Supply From Ignition Switch
^ Switch OFF ignition.
^ Disconnect connector at ignition switch.
^ Turn ignition key to position II.
^ First connect ohmmeter between terminals 15 and 30, then between terminals 15 and second terminal 30.

Instrument should indicate approx. 0 ohms in both cases.

If reading is correct:
- Proceed to: Checking Supply to Ignition Switch.
If reading is incorrect:
- Try with new ignition switch.





Checking Supply to Ignition Switch
^ Switch OFF ignition.
^ Disconnect ignition switch connector.
^ First connect voltmeter between terminal 30 and ground, then between second terminal 30 and ground.

Instrument should indicate battery voltage in both cases.

If reading is correct:
- Check lead between ignition switch connector terminal 15 and fuse No. 1 for open-circuit.
If reading is incorrect:
- Check lead between battery positive terminal and ignition switch connector terminal 30 for open-circuit.