Turn ignition switch to "OFF" position. Ensure all procedures of PREPARATION and EQUIPMENT HOOKUP have been followed. Engine should be at normal operating temperature.
Ensure VOM or tester is connected properly. Turn ignition on. If Star Tester is being used latch center button in down position at this time.
NOTE: DO NOT depress throttle during KOEO SELF-TEST.
The ECA will run through a test cycle, opening and closing various solenoids and switches. After the completion of the test cycle the codes will appear Record all codes.
The first set of codes to appear are the KOEO SELF-TEST codes, they will be repeated twice followed by the Separator Pulse signal and then the CONTINUOUS MEMORY codes. These codes will also be repeated twice.
A KOEO code 11 indicates the system has passed the self test. A code 11 must be present before continuing. Disregard any CONTINUOUS MEMORY codes at this time. Service KOEO codes (in the order they appear) and rerun KOEO test until a code 11 is displayed. See KOEO SELF-TEST service code tables.
Whenever a repair is made, repeat QUICK TEST. If no codes are displayed, repeat SELF-TEST to verify that other service codes are still present.

SERVICE CODES

Code	Description
11	System Passes Test Procedure
12	Unable To Control RPM During Self-test High RPM Check
13	Unable To Control RPM During Self-test Low RPM check
14	Profile Ignition Pickup (PIP) Circuit Failure
15	Electronic Control Assembly (ECA) ROM Test Failure
18	Spark Output Signal from ECC-IV Processor (SPOUT) Circuit Open
19	Failure In EEC Internal Voltage
21	Engine Coolant Temperature (ECT) Sensor Out Of Range
22	Manifold Absolute Pressure (MAP) Signal Out Of Range
23	Throttle Position Sensor (TPS) Signal Out Of Range
24	Air Charge Temperature (ACT) Sensor/Signal Out Of Range
39	AXOD Converter By-pass Clutch Not Applying Properly
41	Heated Exhaust Gas Oxygen (HEGO) Sensor Circuit Indicates System Lean
51	Engine Coolant Temperature (ECT) Sensor Circuit Grounded
53	Throttle Position Sensor (TPS) Circuit Above Maximum Voltage
54	Air Charge Temp. (ACT) Sensor Indicates -40°F/Circuit Open
57	Neutral Pressure Switch Failed Open
59	AXOD 4-3 Pressure Switch Circuit Failed Open
61	Engine Coolant Temperature (ECT) Sensor Circuit Grounded
62	AXOD 4-3 Or 3-2 Pressure Switch Circuit Failed Closed
63	Throttle Position Sensor (TPS) Circuit Below Minimum Voltage
64	Air Charge Temperature (ACT) Sensor Circuit Grounded
67	Neutral Pressure Switch (NPS) Circuit Open; A/C On
68	AXOD Transmission Temperature Switch (TTS) Circuit Failed Open
69	AXOD 3-4 Pressure Switch Circuit Failed Open
73	Insufficient Throttle Position Sensor (TPS) Output Charge During Dynamic Response Test
75	Brake On/Off (BOO) Switch Always Closed, Or Signal
89	AXOD Lock Up Solenoid Circuit Failed

NOTE: Not all testing information for ELECTRICAL SYSTEM TESTING is included in this article. See appropriate TESTS W/CODES article in ENGINE PERFORMANCE.

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

Test Procedure

Use the Manual With the Right Hardware

When to See a Mechanic

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