Hard Failures
Hard failures cause Malfunction Indicator Light (MIL) to come on and remain on until problem is repaired. If MIL comes on and remains on (light may flash) during vehicle operation, cause of malfunction must be determined by using diagnostic (code) charts. If a sensor fails, PCM will use a substitute value in its calculations to permit continued engine operation. In this condition (limp-in mode), vehicle will run but driveability will not be optimum.
Intermittent Failures
Intermittent failures may cause MIL to flicker or come on and go off after intermittent defect goes away. Corresponding trouble code, however, will be retained in PCM memory. If related defect does not reoccur within a certain time, related trouble code will be erased from PCM memory. Intermittent failures may be caused by a sensor, connector, or wiring. See INTERMITTENTS in TESTS W/O CODES article.
VISUAL CHECK & VEHICLE PREPARATION
Before connecting any equipment to diagnose electronic engine control system, perform following preparatory procedures
- Verify condition of air cleaner and air ducts.
- Inspect all vacuum hoses for leaks, restrictions, or improper routing.
- Inspect electrical system for corrosion, bent or broken pins, loose wires or terminals, or improper routing.
- Inspect PCM, sensors, and actuators for physical damage.
- Check engine oil and coolant level.
- Observe all necessary safety precautions to prevent personal injury or vehicle damage.
- Set parking brake. Position shift lever into Park for automatic transmissions, or Neutral for manual transmissions. DO NOT move shift lever during test unless specifically directed.
- Turn off all lights and accessories. Ensure vehicle doors are closed when measuring voltage or resistance.
- Start engine. Run at idle until upper radiator hose is hot and pressurized and engine is off fast idle. Inspect for leaks around exhaust manifold, exhaust gas oxygen sensor, and vacuum hose connections.
- Turn ignition off. Service items as required. Go to EQUIPMENT HOOK-UP.
VOM
1) Turn ignition off. Connect a jumper wire from STI connector to ground. Refer to SELF-TEST CONNECTOR LOCATION and SELF-TEST CONNECTOR WIRE COLORS tables. (Scheme 14)
Scheme 14
2) Connect VOM between STO terminal and engine ground. Set VOM to measure 0-20 volts DC.
MIL
Connect jumper wire between STI connector and ground.
NGS Or Super Star II Tester
Connect instrument according to manufacturer's instructions.
| Application | Location |
|---|---|
| Aspire | LR Corner Engine Compartment |
SELF-TEST CONNECTOR LOCATION
| Circuit | Wire Color |
|---|---|
| PCM STO | White/Black |
| SML | Blue/Black |
| STI | Blue |
SELF-TEST CONNECTOR WIRE COLORS
Reading Service Codes
Engine control system communicates malfunctions to technician through service codes. These service codes are 2-digit numbers representing a particular defect. Service codes are transmitted through STO connector.
Service codes are displayed as timed pulses, and may be read with a VOM, NGS, or Super Star II tester. VOM displays codes by needle sweeps. (Scheme 15)
Turn ignition off. Follow all procedures of EQUIPMENT HOOK-UP. Engine should be at normal operating temperature.
Disconnect and reconnect jumper wire from STI terminal to ground. Turn ignition on. Record displayed codes. Erase codes, then repeat test procedure to verify all codes are currently valid. See ERASING CODES & RETESTING . Service only those codes which appear during retest. Refer to TROUBLE CODE IDENTIFICATION table to find appropriate pinpoint test.
Turn ignition on. Connect jumper wire between STI connector and ground. Observe MIL, and record pulses to determine codes stored.
Scheme 15
Note. If MIL flashes continuously prior to connecting test equipment, go to PINPOINT TEST STI.
Follow manufacturer's instructions to retrieve codes.
ERASING CODES & RETESTING
Erasing codes and retesting will give an indication of whether codes are hard or intermittent defects. Hard codes reset immediately and will be displayed during retest.
Disconnect negative battery cable. Press brake pedal for 5-10 seconds. Turn off NGS or Super Star II tester. Reconnect battery. Perform tests under RETRIEVING CODES to again display and record codes.
Clearing Codes Procedure
Disconnect negative battery cable. Press brake pedal for 5-10 seconds. Turn off VOM or Super Star II tester. Reconnect battery.
Connect and operate tester according to manufacturer's instructions. Operate each switch listed in SWITCH MONITOR TEST table. Note output as each switch operates. Record test results.
1) Ground STI connector. Connect VOM positive lead to SML terminal on self-test connector. Connect negative lead to ground. (Scheme 14)
2) Operate each switch listed in SWITCH MONITOR TEST table. Note output on VOM as each switch is operated. Go to specified PINPOINT TEST if any switch does not meet specification.
Note. Do not move throttle, clutch, or transmission range selector lever unless so directed.
| Switch | VOM Indication/Condition | (1) Pinpoint Test |
|---|---|---|
| A/C Switch | Less Than 1.5 Volts; A/C & Blower Switch On | STG |
| Blower Motor Switch | Less Than 1.5 Volts; Switch Set To "2" Or Higher | STG |
| Brake On/Off Switch | Less Than 1.5 Volts; Brake Pedal Partially Pressed | STP |
| Clutch Engage/Neutral Gear Switch (2) | Less Than 1.5 Volts; In Gear, Clutch Released | STG |
| Coolant Temp. Switch | Less Than 1.5 Volts; Cooling Fan On | STP |
| Cooling Fan Relay | Less Than 1.5 Volts; Accelerator Pedal Pressed (3) | ROC |
| Defrost Switch | Less Than 1.5 Volts; Defrost Switch On | STP |
| Headlight Switch | Less Than 1.5 Volts; Headlight Switch On | STP |
| Idle Switch | Less Than 1.5 Volts; Accelerator Pedal Pressed | STG |
| Transmission Range Switch | Less Than 1.5 Volts; Transaxle In Gear | STP |
| (1) Proceed to specified PINPOINT TEST if indication is incorrect. (2) Not applicable to vehicles with A/T. (3) Fan should operate. | ||
| (1) | Proceed to specified PINPOINT TEST if indication is incorrect. |
| (2) | Not applicable to vehicles with A/T. |
| (3) | Fan should operate. |
SWITCH MONITOR TEST
PINPOINT TESTS
Note. Following tests and illustrations are courtesy of Ford Motor Co. Complete EEC system WIRING DIAGRAMS may be found in WIRING DIAGRAMS section.
HOW TO USE PINPOINT TESTS
Note. Inspect all wiring, harnesses, connectors, and components for damage, overheating, shorting, or looseness. If any defect is found, repair as necessary before proceeding to any PINPOINT TEST.
1) Perform PINPOINT TEST only if directed to do so by a QUICK TESTS procedure. Repair all non-EEC related defects. Follow each test step in order until defect is found. DO NOT replace any part unless so directed. When more than one service code exists, start with first code displayed.
2) PINPOINT TESTS require that electrical circuits are okay before replacing sensors or any other components. Always test circuits for continuity between sensor and PCM. Test all circuits for shorts to voltage, opens, or shorts to ground. VREF and VPWR circuits should be tested with KOEO or as specified in PINPOINT TESTS.
3) DO NOT measure voltage or resistance at PCM, or connect any test light unless specified in test procedure. DO NOT pierce wiring. Isolate both ends of a circuit and turn ignition off before testing for shorts or continuity, unless otherwise specified.
4) Disconnect solenoids and switches before testing for circuit continuity or energizing solenoids.
5) An open is defined as any resistance greater than 10,000 ohms, unless otherwise specified.
6) To help diagnose circuits to PCM, turn ignition off and disconnect PCM harness. Connect BOB between PCM and PCM harness to perform circuit and pinpoint tests.
SUMMARY
If no hard codes, or only pass codes, exist and driveability symptoms or intermittent codes still exist, proceed to TESTS W/O CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.
