Part 1

DIAGNOSTIC ITEM 2: Diagnose shorts in the ground to CAN bus line

CAUTION:
When servicing a CAN bus line, ground yourself by touching a metal object such as an unpainted water pipe. If you fail to do so, a component connected to the CAN bus line may be damaged.

FUNCTION

When diagnosing the CAN bus lines, the scan tool MB991958 measures the voltage of CAN_H and CAN_L line and detects the short to ground.

TROUBLE JUDGMENT CONDITIONS

The scan tool MB991958 judges the trouble when it is impossible to receive the periodically sent data and the voltage of CAN_H or CAN_L line is less than 1.0 volt.

TROUBLESHOOTING HINTS

- The wiring harness may be defective (CAN bus lines for short to ground)
- The connectors may be defective (short to ground in the connector)
- Each ECU may be defective (short to ground in the ECU)

DIAGNOSIS

Required Special Tools:

- MB991223: Harness Set
- MB992006: Extra Fine Probe
- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: Vehicle Communication Interface (V.C.I.)
- MB991827: M.U.T.-III USB Cable
- MB991910: M.U.T.-III Main Harness A
- MB991923: Power plant ECU Check Harness
- MB991997: ASC Check Harness

STEP 1. Check the CAN bus lines for short to ground. Measure the resistance at data link connector C-125.

CAUTION:

- A digital multimeter should be used. For details refer to Precautions When CAN Bus Line(s) are Repaired .
- The test wiring harness should be used. For details refer to Precautions When CAN Bus Line(s) are Repaired .

NOTE:
This inspection allows you to check that there is a short to ground in either CAN_H line or CAN_L line.

(1)
CAUTION:
Disconnect the negative battery terminal. For details refer to Precautions When CAN Bus Line(s) are Repaired.

Disconnect the negative battery terminal.

(2)Disconnect ECM [M/T] or PCM [A/T] connector B-18 and combination meter connector C-04, and measure the resistance at the harness side of data link connector C-125.

(3)Measure the resistance between data link connector terminal 6 (CAN_H) and body ground.
OK: 1 kohms or more

(4)Measure the resistance between data link connector terminal 14 (CAN_L) and body ground.
OK: 1 kohms or more

Q. Is the check result normal?

YES Go to Step 21.

NO Go to Step 2.

STEP 2. Check the CAN bus line of the front wiring harness for short to ground. Measure the resistance at intermediate connector C-24 [ECLIPSE] or C-23 [ECLIPSE SPYDER].

(1)
CAUTION:
Disconnect the negative battery terminal. For details refer to Precautions When CAN Bus Line(s) are Repaired.

Disconnect the negative battery terminal.

(2)Disconnect intermediate connector C-24 [ECLIPSE] or C-23 [ECLIPSE SPYDER], and measure the voltage at the male side (at front wiring harness side [ECLIPSE] or floor wiring harness side [ECLIPSE SPYDER]).

(3)Measure the resistance between intermediate connector (C-24) terminal 11 (CAN_H) and body ground. [ECLIPSE]
OK: 1 kohms or more

(4)Measure the resistance between intermediate connector (C-24) terminal 12 (CAN_L) and body ground. [ECLIPSE]
OK: 1 kohms or more

(5)Measure the resistance between intermediate connector (C-23) terminal 22 (CAN_H) and body ground. [ECLIPSE SPYDER]
OK: 1 kohms or more

(6)Measure the resistance between intermediate connector (C-23) terminal 23 (CAN_L) and body ground. [ECLIPSE SPYDER]
OK: 1 kohms or more

Q. Is the check result normal?

YES : Go to Step 3.

NO [ECLIPSE] : Go to Step 15.

NO [ECLIPSE SPYDER] : Go to Step 16.

STEP 3. Check the CAN line between joint connector (3) and the combination meter for short to ground. Measure the resistance at joint connector (3) C-03.

(1)
CAUTION:
Disconnect the negative battery terminal. For details refer to Precautions When CAN Bus Line(s) are Repaired.

Disconnect the negative battery terminal.