KOEO & KOER Codes (Hard Faults)
These codes indicate faults are present at time of testing. A hard fault may cause CHECK ENGINE or Malfunction Indicator Light (MIL) to go on and remain on until fault is repaired. If KOEO or KOER codes are retrieved during KOEO SELF-TEST or KOER SELF-TEST, use DIAGNOSTIC TROUBLE CODE REFERENCE CHARTS to find correct testing and repair procedures.
Continuous Memory Codes (Intermittent Faults)
These codes indicate a fault that may or may not be present at time of testing. These codes are used to diagnose intermittent problems. Continuous Memory Codes are retrieved after KOEO SELF-TEST. Some codes may turn on MIL/CHECK ENGINE light. Corresponding intermittent fault trouble code will be retained in PCM memory. If fault does not reoccur within 40 warm-up cycles, PCM will automatically clear code.
After noting and/or repairing fault, clear codes from memory. See CLEARING CODES. Intermittent faults may be caused by a sensor, connector or wiring-related problem. See INTERMITTENTS in TESTS W/O CODES article in the ENGINE PERFORMANCE section.
| CAUTION | Continuous Memory Codes should be recorded when retrieved. These codes may be used to identify intermittent problems that exist after all KOEO and KOER codes have been repaired and a Code 111 (pass code) has been obtained. Some Continuous Memory Code faults may not be valid after KOEO and KOER codes are serviced. |
RETRIEVING CODES
Diagnostic trouble codes are retrieved from EEC-IV system through Data Link Connector (DLC). Various methods and test equipment may be used to access these codes
- Analog Volt-Ohmmeter (VOM)
- Scan Tester
- Malfunction Indicator Light (MIL)/CHECK ENGINE Light
- STAR Series Tester
| Application | Location |
|---|---|
| 2.0L | Left Side Of Engine Compartment, On Fender Apron |
DATA LINK CONNECTOR (DLC) LOCATION
Separator Pulse
Single 1/2-second separator pulse is issued 6-9 seconds after last KOEO code. Continuous Memory Codes (soft faults) are then displayed 6-9 seconds after 1/2-second separator pulse.
Pass Codes
A Code 111 indicates no diagnostic trouble codes were recorded in that portion of test; system passes that portion of test. If Code 111 is not retrieved in KOEO SELF-TEST, codes retrieved during KOER SELF-TEST may not be valid. Code 111 (pass code) must be obtained in KOEO SELF-TEST. A Code 111-1-111 output during KOEO SELF-TEST indicates no KOEO code or Continuous Memory Code was recorded.
Continuous Memory Codes
These codes result from information stored by PCM during continuous self-test monitoring. Codes are displayed after separator pulse code in KOEO SELF-TEST. Use these codes for diagnosis only when KOEO SELF-TEST and KOER SELF-TEST result in Code 111 (pass code) and all steps under QUICK TEST are successfully completed. (A few codes are exceptions which may be checked after KOEO codes have been repaired). These codes indicate faults recorded within last 40 engine starts. Fault may or may not be currently present. See DIAGNOSTIC TROUBLE CODE REFERENCE CHART.
Fast Codes
At start of KOEO SELF-TEST and after Wide Open Throttle (WOT) request in KOER SELF-TEST, PCM outputs short bursts of information, known as FAST CODES, which were used by manufacturer during assembly. These codes contain the identical information as slow codes, but are transmitted at 100 times the normal rate. With most equipment (except Super Star II tester), these code bursts are not visible. An entire code sequence lasts less than 1/2 second.
Scheme 34
CLEARING CODES
To clear codes from PCM memory, start KOEO SELF-TEST. When diagnostic trouble codes appear on test equipment or MIL/CHECK ENGINE light, disconnect jumper wire from Self-Test Input (STI) connector. If using STAR Series Tester, unlatch center button. This procedure erases Continuous Memory Codes from PCM memory. If problem has not been corrected or fault is still present, hard code will immediately be reset in PCM memory.
| CAUTION | DO NOT disconnect vehicle battery to clear codes. This will erase stored operating information from Keep-Alive Memory (KAM). To clear KAM, disconnect negative battery terminal for at least 5 minutes. |
| CAUTION | When battery is disconnected, vehicle computer and memory systems may lose memory data. Driveability problems may exist until computer systems have completed a relearn cycle. See COMPUTER RELEARN PROCEDURES article in GENERAL INFORMATION section before disconnecting battery. |
VISUAL CHECK
Complete all steps in BASIC TESTING article in the ENGINE PERFORMANCE section before proceeding to self-diagnostic tests. Ensure all vacuum hoses and EEC-IV wiring harnesses are properly connected.
EQUIPMENT HOOKUP
Apply parking brake, and place shift lever in Park position. Block drive wheels. Turn off all electrical accessories. Connect appropriate test equipment to vehicle as follows
Analog Volt-Ohmmeter (VOM)
1) Turn ignition off. Set VOM at 0-15V DC range. Connect positive lead of VOM to positive battery terminal.
2) Connect negative VOM lead to Self-Test Output (STO) terminal of Data Link Connector (DLC). (Scheme 35) Go to KOEO SELF-TEST. Activate KOEO SELF-TEST by connecting jumper wire from Self-Test Input (STI) pigtail to signal return (SIG RTN) terminal at DLC with ignition on.
Scan Tester
Follow manufacturer's instructions to hook up equipment and record diagnostic trouble codes.
STAR Series Tester
Turn ignition off. Connect color-coded adapter cable leads to diagnostic tester. Connect 2 service connectors of adapter cable to vehicle Data Link Connector (DLC) and STI pigtail connector. Go to KOEO SELF-TEST.
CHECK ENGINE Light/Malfunction Indicator Light (MIL)
Turn ignition on. Connect a jumper wire between Self-Test Input (STI) pigtail and signal return (SIG RTN) terminal of Data Link Connector (DLC). (Scheme 35) Go to KOEO SELF-TEST.
Scheme 35
ADDITIONAL SYSTEM FUNCTIONS
Additional diagnostic system features are available to help diagnose driveability problems and service EEC-IV systems.
Malfunction Indicator Light (MIL)
MIL are intended to alert driver of certain malfunctions in EEC-IV system. Light may also be used to retrieve diagnostic trouble codes stored in PCM. When hooked up for KOEO SELF-TEST or KOER SELF-TEST, light will display all codes which turn on light during vehicle operation.
Light should come on when ignition is turned on and go out when engine is started. If light comes on and then goes off during vehicle operation, code causing light to come on will be stored in PCM memory as a Continuous Memory Code. If light comes on during vehicle operation, vehicle should be inspected as soon as possible. Immediately turning off engine is not necessary; vehicle can be driven with light on.
Output State Check
Output state check is used as an aid in servicing output actuators associated with EEC-IV system. It allows technicians to energize and de-energize most system output actuators on command. This mode is entered from KOEO SELF-TEST after all codes have been retrieved.
Disconnect cruise control servo (if equipped). With DVOM on 20-volt scale, connect DVOM negative lead to STO terminal at Diagnostic Link Connector (DLC). Connect positive lead to positive battery terminal. Using jumper wire, connect STI to SIG RTN at Diagnostic Link Connector (DLC).
Perform KOEO SELF-TEST until continuous memory test is complete. DVOM will read less than 1.0 volt when test is complete. Depress and release throttle. If voltage increases, OUTPUT STATE CHECK has been entered. If voltage does not increase, depress throttle to WOT and release. If STO voltage still does not increase, go to CIRCUIT TEST QC.
Failure Mode Effects Management (FMEM) Code 998
FMEM mode allows system operation when sensors fail or transmit signals that are out of normal operating range. During FMEM mode, PCM substitutes a mid-range signal for defective sensor while continuing to monitor sensor. If faulty sensor's signals return to normal operating range, PCM will use those signals. A Code 998 will be displayed when FMEM mode is in effect.
CIRCUIT TESTS
Note. A breakout box, connected to vehicle harness at PCM, is necessary to perform most circuit tests. References to Test Pin No. found in CIRCUIT TEST steps refer to test terminals on manufacturer's breakout box. Circuit diagrams at beginning of each test identify circuit and wire colors.
HOW TO USE CIRCUIT TESTS
1) Ensure all non-EEC related faults found while performing steps in BASIC TESTING article in the ENGINE PERFORMANCE section have been corrected. DO NOT perform any CIRCUIT TEST unless specifically instructed by a QUICK TEST procedure. Follow each test step in order until fault is found. DO NOT replace any part unless directed to do so. When more than one code is retrieved, start with first code displayed.
2) CIRCUIT TESTS ensure electrical circuits are okay before sensors or other components are replaced. Always test circuits for continuity between sensor and PCM. Test all circuits for short to power, opens or short to ground. Voltage Reference (VREF) and Voltage Power (VPWR) circuits should be tested with ignition on or as specified in CIRCUIT TESTS.
3) DO NOT measure voltage or resistance at PCM. DO NOT connect any test light unless specified in testing procedure. All measurements are made by probing rear of connector (wiring harness side). Isolate both ends of a circuit and turn ignition off when checking for shorts or continuity, unless instructed otherwise.
4) Disconnect solenoids and switches from harness before measuring continuity and resistance or applying voltage. After each repair, check all component connections and repeat QUICK TEST.
5) An open circuit is defined as a resistance reading of greater than 5 ohms. This specification tolerance may be too high for some items in EEC-IV system. If resistance approaches 5 ohms, always clean suspect connector and coat it with protective dielectric silicone grease. A short is defined as a resistance reading of 10,000 ohms or less, unless stated otherwise in CIRCUIT TEST.
Note. In following tests, circuit diagrams and illustrations are courtesy of Mazda Motors Corp.
CIRCUIT TESTS are grouped as follows
- AA-C - No Start & Voltage Tests.
- DA-DR - Input Sensor Tests.
- FD-FF - Additional Input Component Tests.
- G-J - Fuel Control Systems.
- KD-TC - PCM (Processor) Output Tests.
Preliminary Instructions
Record and clear continuous memory codes. Warm engine to normal operating temperature. Place gear selector in Drive position. Accelerate hard to 35 MPH and coast down to a stop. Shut off engine. Perform KOEO SELF-TEST. Go to step 1).
1) Continuous Memory Code 452 Code 452 indicates PCM detected incorrect output from VSS sometime during vehicle operation. Possible causes for this code are
- Faulty VSS.
- Open or shorted circuit.
- Faulty PCM.
Perform appropriate drive cycle procedure. See PRELIMINARY INSTRUCTIONS. Ensure driveability complaint can be verified. If Code 452 is still present or driveability complaint can be verified, go to next step. If code is not present or complaint cannot be verified, fault cannot be duplicated at this time. Clear codes, and see SYMPTOMS in TESTS W/O CODES article in the ENGINE PERFORMANCE section.
2) Check VSS Circuit Continuity Turn ignition off. Disconnect VSS sensor. Remove PCM 60-pin connector. Inspect connector for damaged pins, corrosion and loose wires. Repair as necessary. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving PCM connector disconnected. Measure resistance between VSS (+) terminal at VSS wiring harness connector and test pin No. 3 at breakout box. Also, measure resistance between VSS (-) terminal at VSS wiring harness connector and test pin No. 6 at breakout box. If any resistance reading is more than 5 ohms, repair open circuit in VSS wiring harness. Remove breakout box reconnect all components. Repeat step 1). If both resistance readings are 5 ohms or less, go to next step.
3) Check VSS Circuits For Shorts To Power Or Ground Turn ignition off. Ensure PCM and VSS are disconnected. Measure resistance between test pin No. 3 and test pins No. 6, 37 and 40 at breakout box. If all readings are more than 500 ohms, go to next step. If any reading is 500 ohms or less, repair shorts in VSS wiring harness and repeat step 1).
4) Check VSS Resistance Turn ignition off. Disconnect VSS wiring harness connector. Measure resistance between VSS terminals. If resistance is not 190-250 ohms, replace VSS and repeat step 1). If resistance is 190-250 ohms, replace PCM and repeat step 1).
SUMMARY
If no diagnostic trouble code is present but driveability problem still exists, proceed to TESTS W/O CODES article in the ENGINE PERFORMANCE section for symptom diagnostic or intermittent diagnosis procedures.