Check Mode Procedure

Total OBD & ECU Auto Diagnostics

Total OBD & ECU Auto Diagnostics

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Intelligent tester only:

Compared to normal mode, check mode is more sensitive to malfunctions. Therefore, check mode can detect the malfunctions that cannot be detected by normal mode. NOTICE:

All the stored DTCs and freeze frame data are erased if: 1) the ECM is changed from normal mode to check mode or vice versa; or 2) the ignition switch is turned from ON to ACC or OFF while in check mode. Before changing modes, always check and make a note of any DTCs and freeze frame data.

1. CHECK MODE PROCEDURE (Using the intelligent tester)

(a) Check and ensure the following conditions:

(1) Battery voltage 11 V or more

(2) Throttle valve fully closed

(3) Transmission in the P or N positions

(4) A/C switched OFF

(b) Turn the ignition switch to OFF.

(c) Connect a intelligent tester to the DLC3.

(d) Turn the ignition switch to ON.

(f) Select the following menu items: DIAGNOSIS / ENHANCED OBD II / CHECK MODE.

(g) Switch the ECM from normal mode to check mode.

■0.13 seconds



0.13 seconds '


(h) Make sure the MIL flashes as shown in the illustration.

(i) Start the engine.

(j) Make sure the MIL turns off.

(k) Simulate the conditions of the malfunction described by the customer. (l) Check DTCs and freeze frame data using the tester.


If any of the following DTCs are set, the ECM enters fail-safe mode to allow the vehicle to be driven temporarily.



Fail-Safe Operations

Fail-Safe Deactivation Conditions

P0031 and P0032

Air-Fuel Ratio (A/F) Sensor Heater

ECM turns off A/F sensor heater.

Ignition switch OFF

P0037 and P0038

Heated Oxygen (HO2) Sensor Heater

ECM turns off HO2 sensor heater

Ignition switch OFF

P0100, P0102 and P0103

Mass Air Flow (MAF) Meter

ECM calculates ignition timing according to engine speed and throttle valve position.

Pass condition detected

P0110, P0112 and P0113

Intake Air Temperature (IAT) Sensor

ECM estimates IAT to be 20°C (68° F).

Pass condition detected

P0115, P0117 and P0118

Engine Coolant Temperature (ECT) Sensor

ECM estimates ECT to be 80°C (176° F).

Pass condition detected

P0120, P0121, P0122, P0123, P0220, P0222, P0223, P0604, P0606, P0607, P0657, P2102, P2103, P2111, P2112, P2118, P2119 and P2135

Electronic Throttle Control System (ETCS)

ECM cuts off throttle actuator current and throttle valve returned to 6.5° throttle position by return spring.

ECM then adjusts engine output by controlling fuel injection (intermittent fuel-cut) and ignition timing in accordance with accelerator pedal opening angle, to allow vehicle to continue at minimal speed.*

Pass condition detected and then ignition switch turned OFF

P0327 and P0328

Knock Sensor

ECM sets ignition timing to maximum retard.

Ignition switch OFF

P0351 to P0354


ECM cuts fuel.

Pass condition detected

P2120, P2121, P2122, P2123, P2125, P2127, P2128 and P2138

Accelerator Pedal Position (APP) Sensor

APP sensor has 2 sensor circuits: Main and Sub.

If either of circuits malfunctions, ECM controls engine using other circuit.

If both of circuits malfunction, ECM regards accelerator pedal as being released. As a result, throttle valve is closed and engine idles.

Pass condition detected and then ignition switch turned OFF


* The vehicle can be driven slowly when the accelerator pedal is depressed firmly and slowly. If the accelerator pedal is depressed quickly, the vehicle may speed up and slow down erratically.

Tacoma P0113

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