Code No. P1978: Throttle Valve Control Servo Malfunction

OPERATION

Controls the current that is applied from the engine-ECU (terminals No. 7, No. 22) to the electronic-controlled throttle valve (terminals No. 5, No. 6).

FUNCTION

Engine-ECU check whether the throttle valve control servo magneto failed.

TROUBLE JUDGMENT

Check Condition

Battery positive voltage is 8.3 V or higher.

Judgement Criterion

The throttle actuator is abnormal.

PROBABLE CAUSES

Failed throttle valve control servo.
Open/short circuit and damage in throttle valve control servo circuit or lose connector contact.
Failed engine-ECU

DIAGNOSIS PROCEDURE

STEP 1. Connector check: A-118 electronic-controlled throttle valve connector

Q. Is the check result normal?

Go to Step 2 .

Repair.

STEP 2. Perform resistance measurement at A-118 electronic-controlled throttle valve connector.

Disconnect connector, and measure at electronic-controlled throttle valve side.
Resistance between terminal No. 5 and No. 6.

OK: 0.3 - 100 kΩ (at 20 °C)

Q. Is the check result normal?

Go to Step 3 .

Replace throttle body assembly.

STEP 3. Connector check: A-34 engine-ECU connector

Q. Is the check result normal?

Go to Step 4 .

Repair.

STEP 4. Check harness between A-118 (terminal No. 6) electronic-controlled throttle valve connector and A-34 (terminal No. 7) engine-ECU connector.

Check output line for short circuit and damage.

Q. Is the check result normal?

Go to Step 5 .

Repair.

STEP 5. Check harness between A-118 (terminal No. 5) electronic-controlled throttle valve connector and A-34 (terminal No. 22) engine-ECU connector.

Check output line for short circuit and damage.

Q. Is the check result normal?

Go to Step 6 .

Repair.

STEP 6. Check the trouble symptoms.

Q. Is the check result normal?

	Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).

	Replace engine-ECU then perform the variant coding (Refer to GROUP 00 - Precautions Before Service - How to Perform Variant Coding ).