Diagnosis System

(a) Description

• When troubleshooting OBDII vehicles, the only difference from the usual troubleshooting procedure is that you connect to the vehicle the OBDII scan tool complying with SAE J1978 or TOYOTA handheld tester, and read off various data output from the vehicle's ECM.

• OBDII regulations require that the vehicle's onboard computer lights up the Malfunction Indicator Lamp (MIL) on the instrument panel when the computer detects a malfunction in the emission control system/components or in the powertrain control components which affect vehicle emissions, or a malfunction in the computer. In addition to the MIL lighting up when a malfunction is detected, the applicable Diagnostic Trouble Code (DTC) prescribed by SAE J2012 are recorded in the ECM memory (See page DI-14).

If the malfunction does not reoccur in 3 consecutive trips, the MIL goes off automatically but the DTCs remain recorded in the ECM memory.

• When DTC P3190, P3191 are detected and the remain of the fuel is little, the computer judges the cause as a fuel shortage, and after the next trip, when the supply of fuel is confirmed, it turns off MIL, but the memory of DTC still remains.

To check the DTCs, connect the TOYOTA handheld tester or OBDII scan tool to Data Link Connector 3 (DLC3) on the vehicle. The TOYOTA handheld tester or OBDII scan tool also enables you to erase the DTCs and check freezed frame data and various forms of engine data. (For operating instructions, see the OBDII scan tool's instruction book.) DTCs include SAE controlled codes and manufacturer controlled codes. SAE controlled codes must be set as prescribed by the SAE, while manufacturer controlled codes can be set freely by the manufacturer within the prescribed limits (See DTC chart on page DI-14).

CHECK

FI0534

• The diagnosis system operates in normal mode during normal vehicle use. It also has a check mode for technicians to simulate malfunction symptoms and troubleshoot. Most DTCs use 2 trip detection logic* to prevent erroneous detection, and ensure thorough malfunction detection. By switching the ECM to check mode when troubleshooting, the technician can cause the MIL to light up for a malfunction that is only detected once or momentarily (TOYOTA hand-held tester only). (See step 2)

When a malfunction is first detected, the malfunction is temporarily stored in the ECM memory (1st trip).

If the same malfunction is first detected again during the second drive test, this second detection causes the MIL to light up (2nd trip). (However, the IG switch must be turned OFF between the 1st trip and the 2nd trip.)

Freeze frame data records the engine condition when a misfire (DTC P0300 - P0304) or fuel trim malfunction (DTC P0171, P0172) or other malfunction (first malfunction only), is detected.

• Because freeze frame data records the engine conditions (fuel system, calculated load, engine coolant temperature, fuel trim,engine speed, vehicle speed, etc.) when the malfunction is detected, when troubleshooting it is useful for determining whether the vehicle was running or stopped, the engine warmed up or not, the air-fuel ratio lean or rich, etc. at the time of the malfunction.

Priorities for troubleshooting:

If troubleshooting priorities for multiple DTCs are given in the applicable DTC chart, these should be followed. If no instructions are given troubleshoot DTCs according to the following priorities.

(1) DTCs other than fuel trim malfunction (DTC P0171, P0172), and misfire (DTC P0300 - P0304).

(2) Fuel trim malfunction (DTC P0171, P0172).

N09214

The vehicle's ECM uses ISO 9141-2 for communication. The terminal arrangement of DLC3 complies with SAE J1962 and matches the ISO 9141-2 format.

N09214

Terminal No.

Connection / Voltage or Resistance

Condition

7

Bus ® Line / Pulse generation

During transmission

4

Chassis Ground / ^ Body Ground 1 Q or less

Always

5

Signal Ground / ^ Body Ground 1 Q or less

Always

16

Battery Positive / ^ Body Ground 9 - 14 V

If your display shows "UNABLE TO CONNECT TO VEHICLE" when you have connected the cable of the TOYOTA hand-held tester or OBDII scan tool to DLC3, turned the ignition switch ON and operated the scan tool, there is a problem on the vehicle side or tool side.

• If communication is normal when the tool is connected to another vehicle, inspect DLC3 on the original vehicle.

• If communication is still not possible when the tool is connected to another vehicle, the problem is probably in the tool itself, so consult the Service Department listed in the tool's instruction manual.

2. INSPECT DIAGNOSIS (Normal Mode)

(a) Check the MIL

(1) The MIL comes on when the ignition switch is turned ON and the engine is not running.

HINT:

If the MIL does not light up, troubleshoot the combination meter (See page BE-42).

(2) When the engine started, the MIL should go off. If the lamp remains on, the diagnosis system has detected a malfunction or abnormality in the system.

• If there is no DTC in the normal mode, check the 1st trip DTC using Continuous Test Result function (Mode 7 for SAE J1979) or the TOYOTA hand-held tester or OBDII scan tool.

• TOYOTA hand-held tester only:

When the diagnosis system is switched from normal mode to check mode, it erases all DTCs and freezed frame data recorded in normal mode. So before switching modes, always check the DTCs and freezed frame data, and note them down.

(1) Prepare the TOYOTA hand-held tester or OBDII scan tool (complying with SAE J1978).

(2) Connect the TOYOTA hand-held tester or OBDII scan tool to DLC3 under the instrument panel lower pad.

(3) Turn the ignition switch ON and turn the TOYOTA hand-held tester or OBDII scan tool switch ON.

(4) Use the TOYOTA hand-held tester or OBDII scan tool to check the DTCs and freezed frame data; note them down. (For operating instructions, see the OBDII scan tool's instruction book.)

(5) See step 4 to confirm the details of the DTCs. NOTICE:

• When simulating symptoms with an OBDII scan tool (excluding TOYOTA hand-held tester) to check the DTCs, use normal mode. For code on the DTC chart subject to "2 trip detection logic", perform the following either action.

• Turn the ignition switch OFF after the symptom is simulated the first time. Then repeat the simulation process again. When the problem has been simulated twice, the MIL lights up and the DTCs are recorded in the ECM.

• Check the 1st trip DTC using Mode 7 (Continuous Test Results) for SAE J1979.

The DTCs and freezed frame data will be erased by either action.

(1) Operating the TOYOTA hand-held tester or OBDII scan tool (complying with SAE J1978) to erase the codes. (See the OBDII scan tool's instruction book for operating instructions.)

(2) Disconnecting the battery terminals or EFI fuse. NOTICE:

If the TOYOTA hand-held tester switches the ECM from the normal mode to the check mode or vice-versa, or if the ignition switch is turned from ON to ACC or OFF during check mode, the DTCs and freezed frame data will be erased.

3. INSPECT DIAGNOSIS (Check Mode)

TOYOTA hand-held tester only:

Compared to the normal mode, the check mode has an increased sensitivity to detect malfunctions. Furthermore, the same diagnostic items which are detected in the normal mode can also be detected in the check mode. Check the DTC

(1) Initial conditions:

• Battery positive voltage 11 V or more.

• Throttle valve fully closed.

• Transmission in "P" or "N" position.

(2) Turn the ignition switch OFF.

(3) Prepare the TOYOTA hand-held tester.

(4) Connect the TOYOTA hand-held tester to DLC3 under the instrument panel lower pad.

(5) Turn the ignition switch ON and switch the TOYOTA hand-held tester ON.

(6) Switch the TOYOTA hand-held tester normal mode to check mode. (Check that the MIL flashes.)

NOTICE:

If the TOYOTA hand-held tester switches the ECM from the normal mode to the check mode or vice-versa, or if the ignition switch is turned from ON to ACC or LOCK during check mode, the DTCs and freezed frame data will be erased.

(7) Switch the engine. (The MIL goes out after the engine start.)

(8) Simulate the conditions of the malfunction described by the customer.

NOTICE:

Leave the ignition switch ON until you have checked the DTC, etc.

(9) After simulating the malfunction conditions, use the TOYOTA hand-held tester diagnosis selector to check the DTCs and freezed frame data, etc.

HINT:

Take care not to turn the ignition switch OFF. Turning the ignition switch OFF switches the diagnosis system from check mode to normal mode. so all DTCs, etc. are erased.

(10) After checking the DTC, inspect the applicable circuit.

Was this article helpful?

0 0
Do It Yourself Car Diagnosis

Do It Yourself Car Diagnosis

Don't pay hundreds of dollars to find out what is wrong with your car. This book is dedicated to helping the do it yourself home and independent technician understand and use OBD-II technology to diagnose and repair their own vehicles.

Get My Free Ebook


Post a comment