Diagnosis System

1. DESCRIPTION

(a) When troubleshooting OBD II vehicles, the only difference from the usual troubleshooting procedure is to connect an OBD II scan tool complying with SAE J1987 or a intelligent tester to the vehicle, and read off various data output from the vehicle's ECM.

(b) OBD II regulations require that the vehicle's onboard computer illuminate the Malfunction Indicator Lamp (MIL) on the instrument panel when the computer detects a malfunction in the computer itself or in the drive system components which affect the vehicle emissions. In addition to illuminating the MIL when a malfunction is detected, the applicable DTCs prescribed by SAE J2012 are recorded in the ECM memory (See page AX-32).

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

(c) To check the DTCs, connect the OBD II scan tool or intelligent tester to the DLC3 of the vehicle. The OBD II scan tool or intelligent tester also enables you to erase the DTCs and check freeze frame data and various forms of engine data (For operating instructions, see the instruction book).

(d) The 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 a manufacturer within the prescribed limits (See page AX-32).

(e) The diagnosis system operates in "normal mode" during the normal vehicle use. In normal mode, "2-trip detection logic" is used to ensure accurate detection of malfunction. "Check mode" is also available to technicians as an option. In check mode, "1-trip detection logic" is used for simulating malfunction symptoms and increasing the system's ability to detect malfunctions, including intermittent malfunction.

(f) *2 trip detection logic: When a malfunction is first detected, the malfunction is temporarily stored in the ECM memory (1st trip). IF the ignition switch is turned off and then turned on (IG) again, and same malfunction is detected again, the MIL will illuminate.

DTC set point

:k : Freeze frame data recorded point

(g) The ECM records vehicle and driving condition information as freeze frame data the moment a DTC is stored. When troubleshooting, freeze frame data can be helpful in determining whether the vehicle was running or stopped, whether the engine was warmed up or not, whether the air/fuel ratio was lean or rich, as well as other data recorded at the time of a malfunction.

(h) The intelligent tester displays freeze frame data recorded at five different points: 1) 3 times before the DTC is set, 2) once when the DTC is set, and 3) once after the DTC is set. The data can be used to simulate the vehicle's condition around the time of the malfunction. The data may be helpful in determining the cause of a malfunction. It may also be helpful in determining whether a DTC is being caused by a temporary malfunction.

:k : Freeze frame data recorded point

2. INSPECT THE DLC3

(a) The vehicle's ECM uses ISO 15765-4for communication. The terminal arrangement of the DLC3 complies with SAE J1962 and matches the ISO 15765-14format.

Terminals of DLC 3

Symbol

Terminal No.

Name

Reference Terminal

Result

Condition

SIL

7

Bus "+" line

5 - Signal ground

Pulse generation

During transmission

CG

4

Chassis ground

Body ground

Below 1 Q

Always

SG

5

Signal ground

Body ground

Below 1 Q

Always

BAT

16

Battery positive

Body ground

11 to 14 V

Always

CANH

6

HIGH-level CAN bus line

CANL

54 to 69 Q

IG switch OFF

CANH

6

HIGH-level CAN bus line

Battery positive

1 MQ or higher

IG switch OFF

CANH

6

HIGH-level CAN bus lineCG

CG

1 kQ or higher

IG switch OFF

CANL

14

LOW-level CAN bus line

Battery positive

1 MQ or higher

IG switch OFF

CANL

14

LOW-level CAN bus line

CG

1 kQ or higher

If your display shows UNABLE TO CONNECT TO VEHICLE when you have connected the cable of the OBD II scan tool or intelligent tester to the DLC3, turned the ignition switch on (IG) and operated the scan tool, there is a problem on the vehicle side or tool side.

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

• If the communication is still impossible 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.

Do It Yourself Car Diagnosis

Do It Yourself Car Diagnosis

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