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Home >> Mazda >> 1995 >> 929 V6-3.0L DOHC >> Repair and Diagnosis >> Powertrain Management >> Computers and Control Systems >> Testing and Inspection >> Initial Inspection and Diagnostic Overview >> Diagnostic Strategies >> Troubleshooting Tips
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Troubleshooting Tips

SERVICE POINTS / OUTLINE




Main Relay (Battery Power)
- If the circuit is open, the engine will not start.
- If the circuit is shorted, the EGI fuse (30A) will burn out.





Room Fuse (Engine Control Module (ECM) Memory Power)
- If the circuit is open, the ECM memory function will not operate, and diagnostic trouble codes for intermittent malfunctions will not be indicated. Also, the learning control will be canceled, but will not produce any particular symptom.
- If the circuit is shorted, the ROOM fuse (15A) will burn out.





Ground (Output Devices, Fuel Injector)
- If either output device ground or a fuel injector ground has an open circuit, no particular symptom will be produced. If the related output device and fuel injector grounds both have open circuits, the engine will not start.

Ground (System, Analogue)
- An open circuit will not produce any particular symptom.





TEN Terminal (Data Link Connector)
- If the circuit is open, the Self-Diagnosis Checker cannot perform diagnostic trouble code checks and switch monitoring checks.
- If the circuit is shorted, the opening amount of the idle air control valve will not change, causing hard starting and rough idle. Also, the ignition timing will be fixed, causing lack of power and poor acceleration. The Self-Diagnosis Checker cannot perform sensor monitoring checks.





MEN Terminal (Data Link Connector)
- If the circuit is open, the Self-Diagnosis Checker monitor light will not illuminate.
- If the circuit is shorted, the Self-Diagnosis Checker monitor light will stay illuminated.





FEN Terminal (Data Link Connector)
- If the circuit is open, the Self-Diagnosis Checker buzzer will not sound during the diagnostic trouble code check.
- If the circuit is shorted, code "88" will keep flashing and the buzzer will continue sounding, preventing a diagnostic trouble code check.





Malfunction Indicator Light (MIL)
- If the circuit is open, the MIL will not illuminate with the ignition switch ON.
- If the circuit is shorted, the MIL will not go out after the engine is started.

INPUT DEVICES




Volume Air Flow Sensor (With Intake Air Temperature Sensor)
- If the temperature sensor (within the volume air flow sensor) or circuit is open or shorted, Diagnostic Trouble Code No. 10 will be output, and the ECM will use the preprogrammed intake air temperature of 20°C (680 F).
- If the intake air temperature sensor system fails, no particular symptom will be noticed.
- If the volume air flow sensor terminal Vs or Vc has an open or short circuit, Diagnostic Trouble Code No. 08 will be output, and the throttle position sensor and closed throttle position switch signal will be used to adjust the basic injection amount as to the following three modes.
1. Closed throttle position switch ON.
2. Small throttle angle.
3. Large throttle angle.








Crankshaft Position Sensor (NE, SGT, SGC Signal)
- If the NE signal circuit is open or shorted, Diagnostic Trouble Code No. 02 will be output.
- If the SGT signal circuit is open or shorted, Diagnostic Trouble Code No. 04 will be output.
- If the SGC signal circuit is open or shorted, Diagnostic Trouble Code No. 03 will be output.





Engine Coolant Temperature Sensor
- If the temperature sensor or circuit is open or shorted, Diagnostic Trouble Code No. 09 will be output, and the ECM will use the preprogrammed temperature of 80°C (176°F).
- A malfunction in the engine coolant temperature sensor system may cause rough idle, engine stalling, or hard starting.





Intake Air Temperature Sensor (Dynamic Chamber)
- If the temperature sensor (in the dynamic chamber) or circuit is open or shorted, Diagnostic Trouble Code No. 11 will be output, and the ECM will use the preprogrammed temperature of 20°C (68°F).
- If the intake air temperature sensor system fails, no particular symptom will be noticed.





Throttle Position Sensor
- If terminal Vref or TVO has an open or short circuit, Diagnostic Trouble Code No. 12 will be output.
- If terminal IDL (closed throttle position switch) or ground has an open circuit, Diagnostic Trouble Code No. 12 will be output.
- In both of the above conditions, the ECM uses the fully open throttle program.
- If the throttle position sensor is not properly adjusted or the throttle position sensor system fails, poor acceleration or shift shock will result.

Closed Throttle Position Switch
- The switch monitor function can confirm the presence of an open or short circuit.
- If the circuit is open, Diagnostic Trouble Code No. 12 will be output.
- If the circuit is open, rough idle or engine stalling may appear because of inoperative IAC valve.
- If the circuit is shorted, fuel will be cut when the accelerator pedal is depressed, causing hunting.





Heated Oxygen Sensor
- If sensor output voltage is not generated (because of an open or short circuit), Diagnostic Trouble Code No. 15 (left bank sensor) and/or 23 (right bank sensor) will be output.
- If the heated oxygen sensor output voltage continues unchanged for 20 seconds. after the engine speed exceeds 1,500 rpm, Diagnostic Trouble Codes No.17 (left bank sensor) and/or 24 (right bank sensor) will be output.
- In the above conditions, no closed loop control will be present and no symptom will be noticed.





Knock Sensor
- If the knock sensor or circuit is open or shorted, Diagnostic Trouble Code No. 05 (left bank) and/or 07 (right bank) will be output.
- In the above conditions, ignition timing is retarded.





Exhaust Gas Recirculation (EGR) Valve Position Sensor / EGR Valve
- If the EGR valve position sensor or circuit is open or shorted, Diagnostic Trouble Code No. 16 will be output.
- In the above conditions, the EGR valve will be fully closed.





Starter Signal
- A lack of starter signal input will cause hard starting.





Power Steering Pressure Switch
- An open or short circuit can cause a momentary drop in engine speed during steering.





Central Processing Unit (CPU)
- The switch monitor function can confirm the presence of an open or short circuit in the headlight switch, front fog light switch or rear window defroster switch.
- An open or short circuit in the CPU circuit can cause a momentary drop in engine speed when the headlights, front fog lights, or rear window defroster is turned ON.





Air Conditioning (A/C) Signal (A/C Amplifier)
- The switch monitor function can confirm the presence of an open or short circuit.
- If the circuit is open, the air conditioner will not operate.
- If the circuit is shorted, the air conditioner will constantly operate while the blower is ON.





Blower Signal (A/C Amplifier)
- The switch monitor function can confirm the presence of an open or short circuit.
- If the circuit is open or shorted, the blower fan speed may momentarily drop when in third gear or higher.





Brake Switch
- The switch monitor function can confirm the presence of an open or short circuit.
- An open or short circuit will produce no particular symptom.





Vehicle Speed Signal (Speedometer)
- If the vehicle speed signal circuit is open or shorted, Diagnostic Trouble Code No. O6 will be output.
- If the circuit is open or shorted, the purge solenoid valve will not operate.





Park/Neutral Position Signal
- If the circuit is open, the engine speed will be slightly low in P and N positions.
- If the circuit is shorted, the engine speed will be slightly high in R, D, S, and L ranges.





Reduce Torque Signal
- If a malfunction occurs in the reduce torque signal, the torque reduction control is inhibited and line pressure remains high at shifting. Shift shock may be slightly strong.





Shift Solenoids A & B, Transmission Control Module (TCM)
- An open or short circuit may cause shift shock.

OUTPUT DEVICES




Fuel Injector
- If the circuit is open, the fuel injector will be inoperative, causing rough idle and misfire.
- If the circuit is shorted, the fuel injector will inject fuel constantly, causing rough idle and misfire.





IGT Signal (Ignition Control Module)
- If no IGT signals are input into the ignition control module because of an open or short circuit, the engine will not start.





Idle Air Control Valve (Bypass Air Control (BAC) Valve)
- If the control valve or circuit has an open or short, Diagnostic Trouble Code No. 34 will be output.
- If the circuit is open, the valve will be fully closed, causing rough idle, engine stall, and acceleration hesitation when engine is cold.
- If the circuit is shorted, the valve will be fully opened and the idle speed will be increased, causing hunting.





Fuel Pump Relay
- If the circuit is open, the engine will not start.
- If the circuit is shorted, the fuel pump will remain operating with the ignition switch ON.





Purge Solenoid Valve
- If the solenoid valve or circuit is open or shorted, Diagnostic Trouble Code No. 26 will be output.
- If the circuit is open or shorted, the solenoid valve will not operate.
- A short circuit may cause an improper air/fuel ratio, causing rough idle and hard starting.





Variable Inertia Charging System (VICS) Solenoid Valve
- If the solenoid valve or circuit is open or shorted, Diagnostic Trouble Code No. 41 will be output.
- If the circuit is open, the solenoid valve will stay OFF and the shutter valve will stay closed, causing a power drop in the high-speed range.
- If the circuit is shorted, the solenoid valve will stay ON and the shutter valve will stay open, causing a power drop in the middle-speed ranges.





EGR Solenoid Valve (Vacuum)
- If the solenoid valve or circuit is open or shorted, Diagnostic Trouble Code No. 28 will be output.
- An open circuit will produce no particular symptom.
- If the circuit is shorted, the solenoid valve will be fully opened, causing engine stall and hard starting.





EGR Solenoid Valve (Vent)
- If the solenoid valve or circuit has an open or short, Diagnostic Trouble Code No. 29 will be output.
- An open or short circuit will produce no particular symptom.





Oxygen Sensor Heater
- If the heater or circuit has an open or short circuit, Diagnostic Trouble Codes No. 36 (right bank heater) and/or 37 (left bank heater) will be output.
- An open or short circuit will produce no particular symptom.





A/C Signal (A/C Relay)
- If the circuit is open, the air conditioner will not operate.
- If the circuit is shorted, the air conditioner will constantly operate while the fan switch is ON.





Cold Start Injector (CSI) Relay
- If the relay or circuit is open or shorted, Diagnostic Trouble Code No. 30 will be output.
- An open circuit will produce no particular symptom.
- A short circuit will make the cold-start injector inoperative, requiring a longer cranking time when the engine is cold.





Barometric Pressure Signal (TCM)
- If the pressure sensor or circuit is open or shorted, the line pressure will not be controlled, causing rough shifting at high altitudes.





A/C Signal (TCM)
- If the A/C signal circuit is open or shorted, Diagnostic Trouble Code No. 65 will be output.
- An open circuit is detected as A/C ON, and the air conditioning will be in the ON mode in D range (NORMAL), and slip lockup will be prohibited.
- A short circuit is detected as A/C OFF, and the air conditioning will be in the OFF mode in D range (NORMAL).





Torque Reduced Signal
- If a malfunction occurs in the torque reduce signal, the torque reduction control is inhibited and the line pressure will remain high when shifting. Shift shock may be slightly strong.




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