Mazda Trucks 1987-1993 Repair Guide

Reading Codes

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Pickup and MPV

Self Diagnosis Checker

A self-diagnosis checker (such as 49-H018-9A1) is used to retrieve code numbers of malfunctions which have happened and were memorized or are continuing. The malfunction is indicated by a code number.

If there is more than one malfunction, the code numbers will display on the self-diagnosis checker one by one in numerical order. In the case of malfunctions, 09, 19, 01, the code numbers are displayed in order of 01, 09 and then 13.

The memory of malfunctions is canceled by disconnecting the negative battery cable.

The ECU had a fail-safe mechanism for the main input sensors. If a malfunction occurs, the emission control unit will substitute values. This will slightly affect the driving performance, but the vehicle may still be driven.

The ECU continuously checks for malfunctions of the input devices during operation. But, the ECU checks for malfunctions of the output devices within three seconds after turning the ignition switch to the ON position and the test connector is grounded.

The malfunction indicator light (MIL) indicates a pattern the same as a self-diagnosis checker when the self-diagnosis check connector is grounded. When the self-diagnosis check connector is not grounded, the lamp illuminates steady while malfunction of the main input sensor occurs and goes out if the malfunction recovers. However the malfunction code is memorized in the emission control unit.

Testing Procedure
SELF-DIAGNOSIS CHECKER
  1. Connect the Self-Diagnosis Checker to the check connector. The check connector is usually located above the right side wheel housing.
  2.  
  3. Set the selector switch on the tester to the A position.
  4.  
  5. Ground the green test connector using a suitable jumper wire.
  6.  
  7. Turn the ignition switch to the ON position. Check that number "88'' flashes on the digital display and the buzzer sounds for three seconds after turning the ignition switch ON.
  8.  
  9. If the number "88'' does not flash, check the main power relay, power supply circuit and check the connector wiring.
  10.  
  11. If the number "88'' flashes and the buzzer sounds continuously for more than 20 seconds, replace the ECU and perform steps 3 and 4 again.
  12.  
  13. Note the code numbers and check the causes. Repair as necessary. Be sure to recheck for code numbers after repairing.
  14.  

MALFUNCTION LIGHT (MIL)
  1. During the self-test a service code is reported by the malfunction indicator light. It will represent itself as a flash on the CHECK ENGINE or SERVICE ENGINE SOON light on the dash panel. A single digit number of 3 will be reported by 3 flashes. However, if a service code is represented by a 3-digit number such as 111, the code will appear on the MIL light as three flashes, then after a two second pause, the light will flash three times.
  2.  
  3. Start the engine and allow it to reach normal operating temperatures.
  4.  
  5. Turn the engine off. Connect a jumper wire from the STI to the SIG RTN at the self test connectors and then turn the ignition switch to the ON position. Service codes will be flashed on the MIL light.
  6.  

NAVAJO



The EEC-IV system may be interrogated for stored codes using the Quick Test procedures. These tests will reveal faults immediately present during the test as well as any intermittent codes set within the previous 80 warm up cycles. If a code was set before a problem self-corrected (such as momentarily loose connector), the code will be erased if the problem does not reoccur within 80 warm-up cycles.

In 1991 the EEC-VI system check from 2 digit codes to 3 digit codes. These codes are obtained the same way and the system functions the same. All of the test procedures apply to both versions of the ECA.

The Quick Test procedure is divided into 2 sections, Key On Engine Off (KOEO) and Key On Engine Running (KOER). These 2 procedures must be performed correctly if the system is to run the internal self-checks and provide accurate fault codes. Codes will be output and displayed as numbers on the hand scan tool, i.e. 23. If the codes are being read through the dashboard warning lamp, the codes will be displayed as groups of flashes separated by pauses. Code 23 would be shown as two flashes, a pause and three more flashes. A longer pause would occur between codes. If the codes are being read on an analog voltmeter, the needle sweeps indicate the code digits in the same manner as the lamp flashes.

In all cases, the codes 11 or 111 are used to indicate PASS during testing. Note that the PASS code may appear, followed by other stored codes. These are codes from the continuous memory and may indicate intermittent faults, even though the system does not presently contain the fault. The PASS designation only indicates the system passes all internal tests at the moment.


CAUTION
To prevent injury and/or property damage, always block the drive wheels, firmly apply the parking brake, place the transmission in P or N and turn all the electrical loads off before performing the Quick Test procedures.

Super Star II Tester
KEY ON ENGINE OFF (KOEO)
  1. Specific instructions for the use of the tester are included with the tester.
  2.  
  3. Plug the tester connectors into the vehicle self-test connectors.
  4.  
  5. Set the switches on the tester to the appropriate settings for type of EEC system and for fast or slow mode. The same information is contained in fast or slow mode, but the fast mode is 100 times faster than the slow and is for use with the Super Star Tester.
  6.  
  7. Turn on the tester power and depress the test button. Turn ON the vehicle ignition key.
  8.  
  9. The tester will read the codes as they exist.
  10.  

KEY ON ENGINE RUNNING (KOER)
  1. Connect the tester as in the KOEO test and start and warm the engine to normal operating temperature.
  2.  
  3. Turn the engine off and depress the test button so it stays in the test position.
  4.  
  5. Restart the engine and the tester will read any existing codes. The tester will display an engine I.D. code, then on some vehicles a Dynamic Response code. The final display will be the service codes.
  6.  

Analog Voltmeter

KEY ON ENGINE OFF (KOEO) AND CONTINUOUS CODES
  1. Turn the vehicle ignition switch to OFF. Set the range of the analog voltmeter to 0-15 volts.
  2.  
  3. Connect the positive lead of an analog voltmeter to the positive of the battery.
  4.  
  5. Connect the negative lead of the voltmeter to the Self-Test Output pin of the Self-Test connector.
  6.  
  7. Connect a jumper wire between the Self-Test Input connector and the Signal Return pin of the Self-Test connector.
  8.  
  9. The needle will sweep 3 times for a code digit of 3, for example. If the code is 123, the needle will sweep once, pause for 2 seconds, sweep twice, pause for 2 seconds, then sweep three times. There will be a 4 second pause between codes. The method of readout of 2 digit codes is similar to the three digit code readout, but only 2 sets of sweeps will occur.
  10.  
  11. The continuous memory codes will be displayed first, then there will be a 6 second pause, a single sweep, anther 6 second pause then the KOEO codes will be displayed.
  12.  

Malfunction Indicator or Check Engine Light

KEY ON ENGINE OFF (KOEO) AND CONTINUOUS CODES
  1. Connect a jumper wire between the Self-Test Input (STI) connector and the Signal Return pin of the Self-Test connector.
  2.  
  3. This will output the codes to the MIL or Check Engine light on the instrument panel.
  4.  
  5. The light will flash 3 times for a code digit of 3, for example. If the code is 123, the light will flash once, pause for 2 seconds, flash twice, pause for 2 seconds, then flash three times. There will be a 4 second pause between codes. The method of readout for 2 digit code is similar to the three digit code readout, but only 2 sets of sweeps will occur.
  6.  
  7. The continuous memory codes will be displayed first, then there will be a 6 second pause, a single flash, another 6 second pause, then the KOEO codes will be displayed.
  8.  

Other Test Modes

CONTINUOUS MONITOR OR WIGGLE TEST MODE

Once entered, this mode allows the technician to attempt to recreate the intermittent faults by wiggling or tapping components, wiring or connectors. The test may by performed during either KOEO or KOER procedures. The test requires the use of either an analog voltmeter or a hard scan tool.

To enter the continuous monitor mode during KOEO testing, turn the ignition switch ON. Activate the test, wait 10 seconds, then deactivate and reactivate the test; the system will enter the continuous monitor mode. Tap, move, or wiggle the harness, component, or connector suspected of causing the problem; if a fault is detected, the code will store in the memory. When the fault occurs, the dash warning lamp will illuminate, the STAR tester will light a red indicator (and possible beep) and the analog monitor needle will sweep once.

To enter this mode in the KOER test:

  1. Start the engine and run it at 2000 rpm for two minutes. This action warms up the oxygen sensor.
  2.  
  3. Turn the ignition switch to OFF for 10 seconds.
  4.  
  5. Start the engine.
  6.  
  7. Activate the test, wait 10 seconds, then deactivate and reactivate the test; the system will enter the continuous monitor mode.
  8.  
  9. Tap, move, or wiggle the harness, component, or connector suspected of causing the problem; if a fault is detected, the code will store in the memory.
  10.  
  11. When the fault occurs, the dash warning lamp will illuminate, the STAR tester will light the red indicator (and possibly beep) and the analog meter needle will sweep once.
  12.  

OUTPUT STATE CHECK

This testing mode allows the operator to energize the de-energize most of the outputs controlled by the EEC-IV system. Many of the outputs may be checked at the component by listening for a click or feeling the item move or engage by a hand placed on the case. To enter this check:

  1. Enter the KOEO test mode.
  2.  
  3. When all codes have been transmitted, depress the accelerator all the way to the floor and release it.
  4.  
  5. The output actuators are now all ON. Depressing the throttle pedal to the floor again switches all the actuator outputs OFF.
  6.  
  7. This test may be performed as often as necessary, switching between ON and OFF by depressing the throttle.
  8.  
  9. Exit the test by turning the ignition switch OFF, disconnecting the jumper at the diagnostic connector or releasing the test button on the scan tool.
  10.  

 
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