ECD SYSTEM, Diagnostic DTC:31

DTC Code DTC Name
31 Air Flow Circuit Malfunction

DESCRIPTION

The air flow meter uses a platinum hot wire. The hot wire air flow meter consists of a platinum hot wire, thermistor and a control circuit installed in a plastic housing. The hot wire air flow meter works on the principle that the hot wire and thermistor located in the intake air bypass of the housing detect any changes in the intake air temperature.

The hot wire is maintained at the set temperature by controlling the current flow through the hot wire. This current flow is then measured as the output voltage of the air flow meter.

The circuit is constructed so that the platinum hot wire and thermistor provide a bridge circuit with the power transistor controlled so that the potential of A and B remains equal to maintain the set temperature.

A01KFDYE01
Text in Illustration
*1 Thermistor *2 Power Transistor
*3 Platinum Hot Wire - -
*a Output Voltage - -
DTC No. DTC Detecting Condition Trouble Area
31 Open or short in air flow meter circuit with more than 3 sec.

  • Open or short in air flow meter circuit

  • Air flow meter

  • ECM

Tech Tips

After confirming DTC No. 31, use the intelligent tester to confirm the air flow ratio from the CURRENT DATA.

Air Flow Value (gm/sec) Malfunction
Approx. 0.0

  • Air flow meter power source circuit open

  • VG circuit open or short
184.0 or more

  • EVG circuit open

WIRING DIAGRAM

A01KHK5E01

INSPECTION PROCEDURE

Tech Tips


  • Read freeze frame data using intelligent tester. Because freeze frame records the engine conditions when the malfunction is detected. When troubleshooting, it is useful for determining whether the vehicle was running or stopped, the engine was warmed up or not, the air-fuel ratio was lean or rich, etc. at the time of the malfunction.

  • When not using the intelligent tester go to step 7.

PROCEDURE


  1. READ VALUE OF INTELLIGENT TESTER (AIR FLOW RATE)


    1. Connect the intelligent tester to the DLC3.

    2. Turn the ignition switch ON and push the intelligent tester main switch ON.

    3. Start the engine.

    4. Read the air flow rate on the intelligent tester.

      Type 1 Type 2
      Air Flow Rata (gm/sec.) 0.0 271.0 or more

    Type2

    CHECK ECM (CHECK CONTINUITY) Click here

    Type1

  2. CHECK INTAKE MASS AIR FLOW METER ASSEMBLY (POWER SOURCE VOLTAGE)


    1. A01KFK0E02

      Disconnect the air flow meter connector.

    2. Turn the ignition switch ON.

    3. Check the voltage between terminals of the air flow meter connector as shown in the table and illustration.

      Voltage

      Terminal

      (Positive terminal ←→ Negative terminal)

      		 Voltage
      +B (1) ←→ Body ground 9 - 14V

    NG

    CHECK WIRE HARNESS

    OK

  3. CHECK ECM (CHECK VOLTAGE)


    1. A01KGF1E03

      Inspect the ECU power source circuit Click here.

    2. Start the engine.

    3. Check the voltage between terminals of the ECM connector as shown in the table and illustration.

      Voltage (Neutral position)

      Terminal

      (Positive terminal ←→ Negative terminal)

      		 Voltage
      VG (E8-19) ←→ E1 (E7-22) 0.5 - 3.0 V

    OK

    CHECK AND REPLACE ECM Click here

    NG

  4. CHECK WIRE HARNESS (ECM - AIR FLOW METER)


    1. A01KGUJE02

      Disconnect the air flow meter connector.

    2. Disconnect the ECM (E8) connector.

    3. Check the continuity between terminals of the air flow meter and ECM connectors as shown in the illustration and table.

      Continuity (Check for open)

      Terminal

      (Air flow meter ←→ ECM)

      		 Standard
      VG (3) ←→ VG (E8-19) Continuity
      E2 (5) ←→ E2 (E8-20)
      Continuity (Check for short)

      Terminal

      (ECM ←→ ECM(Ground))

      		 Standard
      VG (E8-19) ←→ E1 (E7-22) No continuity

    NG

    REPAIR OR REPLACE HARNESS AND CONNECTOR

    OK

    REPLACE INTAKE MASS AIR FLOW METER ASSEMBLY

  5. CHECK ECM (CHECK CONTINUITY)


    1. A01KELVE07

      Check the continuity between terminals of the ECM connectors as shown in the illustration and table.

      Continuity (Check for short)

      Terminal

      (ECM ←→ ECM(Ground))

      		 Standard
      EVG (E8-11) ←→ E1 (E7-22)

      Continuity

      (1 Ω or less)

    NG

    CHECK AND REPLACE ECM Click here

    OK

  6. CHECK WIRE HARNESS (ECM - AIR FLOW METER)


    1. A01KGUJE03

      Disconnect the air flow meter connector.

    2. Disconnect the ECM (E8) connector.

    3. Check the continuity between terminals of the air flow meter and ECM connectors as shown in the illustration and table.

      Continuity (Check for open)

      Terminal

      (Air flow meter ←→ ECM)

      		 Standard
      E2G (2) ←→ EVG (E8-11) Continuity
      Continuity (Check for short)

      Terminal

      (ECM ←→ ECM(Ground))

      		 Standard
      EVG (E8-11) ←→ E1 (E7-22) No continuity

    NG

    REPAIR OR REPLACE HARNESS AND CONNECTOR

    OK

    REPLACE INTAKE MASS AIR FLOW METER ASSEMBLY

  7. CHECK ECM (CHECK VOLTAGE)


    1. A01KGF1E03

      Inspect ECU power source circuit Click here

    2. Start the engine.

    3. Check the voltage between terminals of ECM connector as shown in the table and illustration.

      Voltage (Neutral position)

      Terminal

      (Positive terminal ←→ Negative terminal)

      		 Voltage
      VG (E8-19) ←→ E1 (E7-22) 0.5 - 3.0 V

    OK

    CHECK AND REPLACE ECM Click here

    NG

  8. CHECK INTAKE MASS AIR FLOW METER ASSEMBLY (POWER SOURCE VOLTAGE)


    1. A01KFK0E02

      Disconnect the air flow meter connector.

    2. Turn the ignition switch ON.

    3. Check the voltage between terminals of the air flow meter connector as shown in the table and illustration.

      Voltage

      Terminal

      (Positive terminal ←→ Negative terminal)

      		 Voltage
      +B (1) ←→ Body ground 9 - 14V

    NG

    CHECK WIRE HARNESS

    OK

  9. CHECK WIRE HARNESS (ECM - AIR FLOW METER)


    1. A01KGUJE04

      Disconnect the air flow meter connector.

    2. Disconnect the ECM (E8) connector.

    3. Check the continuity between terminals of the air flow meter and ECM connectors as shown in the illustration and table.

      Continuity (Check for open)

      Terminal

      (Air flow meter ←→ ECM)

      		 Standard
      VG (3) ←→ VG (E8-19) Continuity
      E2 (5) ←→ E2 (E8-20)
      E2G (2) ←→ EVG (E8-11)
      Continuity (Check for short)

      Terminal

      (ECM ←→ ECM(Ground))

      		 Standard
      VG (E8-19) ←→ E1 (E7-22) No continuity
      EVG (E8-11) ←→ E1 (E7-22)

    NG

    REPAIR OR REPLACE HARNESS AND CONNECTOR

    OK

    REPLACE INTAKE MASS AIR FLOW METER ASSEMBLY