Communication Problems With Scan Tool

FAULT TRACING INFORMATION

Fault Sources

^ If engine STARTS:
- Low battery voltage.
- Break in lead to DLC.
- Lead to DLC short circuited to ground.
- Defective wiring in Scan Tool (ST).

^ If engine DOES NOT START:
- Break in 15-feed to ECM.
- Break in 30-feed to ECM.
- Break in feed from main relay to ECM.
- Break in control signal from ECM to main relay.

NOTE: If communication problem occurs when engine started, connect battery charger or extra battery.

TESTING PROCEDURE





Start Engine
^ Test START engine.

If engine starts:
- Proceed to: Check Diagnostic Lead Motronic 1.8, section below
If engine does not start:
- Proceed to: Check Fuse, section below.





Check Diagnostic Lead Motronic 1.8
^ Ignition OFF.
^ Connect an ohmmeter between DLC contact 2 and ground.

Ohmmeter should read approx. 10K ohms.

If value OK:
- Check diagnostic wiring to ST for damage.
If ohmmeter reads approx. 0 ohms:
- Check lead between ECM 55 and DLC contact 2 for short circuit to ground.
If ohmmeter reads Infinite resistance:
- Check lead between ECM 55 and DLC contact 2 for break.





Check Fuse
^ Check if fuse 23 is OK.

If fuse OK:
- Proceed to: Check 15-Feed Before Fuse, section below.
If fuse not OK:
- Check lead between fuse 23 and:
^ ECM 27.
^ AW-ECM contact 14A.
^ both DLC contact 4.
^ main relay contact 1.
for short circuit to ground.





Check 15-Feed Before Fuse
^ Ignition ON.
^ Connect a voltmeter between upper connector on fuse holder to fuse 23 and ground.

Voltmeter should read battery voltage.

If value OK:
- Proceed to: Check 15-Feed After Fuse, section below.
If value differs:
- Check ignition lock.





Check Ignition Lock
^ Ignition OFF.
^ Disconnect connector to Ignition lock.
^ Turn ignition lock to position II.
^ First, connect an ohmmeter between Ignition lock connector contact 15 and contact 30 (to ignition lock) and then between contact 15 and the second contact 30.

In both cases, ohmmeter should read 0 ohms.

If values OK:
- Proceed to: Check Voltage to Ignition Lock, section below.
If any value differs:
- Test with a new ignition lock





Check Voltage to Ignition Lock
^ Ignition OFF.
^ Ignition lock connector disconnected.
^ First connect a voltmeter between Ignition lock connector contact 30 (to battery) and ground and then between second contact 30 and ground.

In both cases voltmeter should read battery voltage.

If values OK:
- Check lead between Ignition lock contact 15 and fuse 23 for break.
If any value differs:
- Check lead between battery positive pole and ignition lock contact 30 for break.





Check 15-Feed After Fuse
^ Ignition OFF.
^ Connect breakout box and check control points.
^ Replace fuse 23.
^ Connect ECM.
^ Ignition ON.
^ Connect a voltmeter between #27 and #19.

Voltmeter should read battery voltage.

If value OK:
- Proceed to: Check 3O-Feed, section below.
If value differs:
- Check lead between fuse 23 and ECM 27 for break.





Check 30-Feed
^ Ignition ON.
^ Breakout box connected.
^ Connect a voltmeter between #18 and #19 on breakout box.

Voltmeter should read battery voltage.

If value OK:
- Proceed to: Check Power Feed From Main Relay, section below.
If value differs:
- Check fuse.





Check Fuse
^ Check if fuse is 24 OK.

If fuse OK:
- Proceed to: Check 30-Feed Before Fuse, section below.
If fuse not OK:
- Check lead between fuse 24 and:
^ ECM 18,
^ AW-ECM contact A3O,
for short circuit to ground.





Check 30-Feed Before Fuse
^ Ignition ON.
^ Connect a voltmeter between upper contact on fuse holder to fuse 24 and ground.

Voltmeter should read battery voltage.

If value OK:
- Check lead between fuse 24 and ECM 18 for break.
If value differs:
- Check lead between battery positive pole and fuse 24 for break.





Check Power Feed From Main Relay
^ Ignition ON.
^ Breakout box connected.
^ Connect a voltmeter between #37 and #19 on breakout box.

Voltmeter should read battery voltage.

If value OK:
- Check all signals to and from ECM.
If value differs:
- Check voltage to main relay contact 3.





Check Voltage to Main Relay Contact 3
^ Ignition OFF.
^ Disconnect main relay.
^ Connect a voltmeter between main relay connector contact 3 (to battery) and ground.

Voltmeter should read battery voltage.

If value OK:
- Proceed to: Check Voltage to Main Relay Contact 2, section below.
If value differs:
- Check lead between main relay contact 3 and battery positive pole for break.





Check Voltage to Main Relay Contact 2
^ Ignition OFF.
^ Main relay disconnected.
^ Connect a voltmeter between main relay connector contact 2 (to battery) and ground.

Voltmeter should read battery voltage.

If value OK:
- Proceed to: Check Control Signal to Main Relay, section below.
If value differs:
- Check lead between main relay contact 2 and battery positive pole for break.





Check Control Signal to Main Relay
^ Ignition ON.
^ Main relay disconnected.
^ Connect a voltmeter between main relay connector contact 1 and battery positive pole.

Voltmeter should read battery voltage.

If value OK:
- Proceed to: Check Voltage From Main Relay, section below.
If value differs:
- Check lead between ECM 36 and main relay contact 1 for break.





Check Voltage From Main Relay
^ Ignition ON.
^ Connect main relay.

Relay should click when connected to connector.

If relay clicks:
- Check lead between ECM 37 and main relay contact 4 for break.
If relay does not click:
- Check signal lead.





Check Signal Lead
^ Ignition OFF.
^ Main relay disconnected.
^ Connect an ohmmeter between main relay connector contact 4 and ground.

If ohmmeter reads approx. 0 ohms:
- Check lead between ECM 37 and main relay contact 4 for short circuit to ground.
- When fault fixed, fit new main relay.

NOTE: This lead also goes to:
^ All Injection valves, contact 1.
^ IAC valves, contact 2.
^ MAF sensor contact 5.
^ EGR vacuum controller contact 2.

If ohmmeter reads more than approx. 0 ohms:
- Test with a new main relay.