Troubleshooting - Snap-on

Appendix B
Troubleshooting
The vehicles listed in the following sections are specific Asian Import models that may have
problems communicating with the scan tool.
B.1 Slow Codes for Many 1988 and Later Mitsubishi,
Chrysler Imports, and Hyundai Sonata
Models with the 2.4L 4-cylinder or the 3.0L V6 SOHC engine transmit data at 63 baud rate. It
may appear that there is a communication problem when actually, data is transmitting at a
very slow speed. The MAIN MENU for these vehicles displays CODES & DATA (SLOW).
Readings from these vehicles take up to seven seconds to change. The baud rate, or “data
update rate” depends on the ECM; it is not controlled by the scan tool.
B.2 Codes & Data for 1989 and Later Toyota Cressida and
Lexus LS400
These vehicles transmit ECM operating data to the scan tool. This test mode appears on the
MAIN MENU as the selection DATA (NO CODES). These Toyota systems do not transmit
trouble codes in this mode. Codes must be read separately by using the CODE FUNCTIONS
selection from the MAIN MENU.
To place the Cressida and Lexus LS400 in a test mode where the ECM is more sensitive to
trouble codes, see “Code Sensitivity—OBD-II and some Pre-OBD-II” on page 231.
For a detailed explanation, refer to Troubleshooter References TA043 and TA044.
B.3 Ford EEC-V Control System on Mazda
These vehicles use a Ford EEC-V control system, which is identical to the system used on
Ford vehicles. Use the US Domestic Vehicle Communication Software and select Ford from
the Manufacturer Selection menu to test this system.
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To test the terminal voltages:
• Test the terminal voltages using a voltmeter. Figure B-1 maps the data link connector.
Refer to Table B-1 for corresponding voltages.
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Appendix B
No Communication for 1987–90 Nissan
A
G
B
H
C
D
I
E
F
J
K
Figure B-1 Data link connector
A—J1850 BUS +
B—CAN medium speed +
C—Case ground
D—Power ground
E— CAN high speed +
F— ISO K-line/KW2000
G—J1850 BUS H—CAN medium speed I— Module programming signal
J— CAN high speed K—Battery B +
Table B-1 Test 16-pin DLC Terminal Voltages
Protocol
Voltage
CAN High speed +
2.5 V
Can High Speed -
2.5 V
Can Medium Speed +
3.0 V
Can Medium Speed -
2.0 V
ISO
7.0 V or greater
KW2000
12.0 V
J1850 +
0.0 V
J1850 -
5.0 V
NOTE: Voltages may vary with BUS terminal activity
B.4 No Communication for 1987–90 Nissan
For a communication problem with 1987–90 Nissan models1, gather codes manually by
placing the ECM in the diagnostic mode and observing two flashing LEDs. This also applies
to 1991 Maxima, Axxess, Van, and Pickup models.
1
478
Except 1987 Sentra and 1990 300ZX.
See “Code Types 07” on page 152 for detailed instructions.
B.5 GM Control Systems on Isuzu and Isuzu-built Geo
Some Isuzu and Isuzu-built Geo models have General Motors control systems. These
vehicles may display a NO COMMUNICATION message when the scan tool and the control
module cannot communicate with each other for some reason. Common problems that
prevent a vehicle from performing a test or communicating with the scan tool are listed below.
If the CHECK ENGINE lamp passes the bulb check, put the ECM into the “field service” mode
by turning the ignition on and jumpering pin B to pin A in the 12-pin ALDL connector, or pin A
to pin C on the 3-pin ALDL connector (Figure B-2).
F
E
D
C
B
A
G
H
J
K
L
M
Figure B-2 Jump these pins to flash codes on the CHECK ENGINE lamp
The CHECK ENGINE lamp should flash code 12 three times. It then flashes any other codes
present in ECM memory, or it flashes code 12 again. Code 12 appears on the CHECK
ENGINE lamp as in Figure B-3.
CHECK ENGINE
Flash
Pause
CHECK ENGINE
CHECK ENGINE
Flash
Flash
Figure B-3 Code 12 on CHECK ENGINE lamp
Several different symptoms and problems may occur at this point:
• If the CHECK ENGINE lamp lights for a bulb check but stays off and does not flash any
codes, check the continuity between pins A and B in the ALDL connector (A and C on the
3-pin connector).
• If the CHECK ENGINE lamp flashes rapidly with no code pattern, check the ECM. Verify
that a PROM is installed. Refer to the troubleshooting procedure for the test vehicle.
• If the CHECK ENGINE lamp lights steadily and does not flash with ALDL pins A and B
jumpered, refer to the factory troubleshooting chart for the specific vehicle.
• Watch for code 51 or other 50-series codes that indicate a PROM or ECM problem. Code
51 means there is either a PROM failure or a missing PROM. Many carbureted engines
do not transmit a code 51 on the data stream; and if the PROM is missing, the ECM for
these systems does not communicate with the scan tool. However, some ECMs do flash
code 51 on the CHECK ENGINE lamp.
Most communication problems can be found and corrected by checking the points listed in
this section. In a few cases, communication failure may be due to ECM failure. In all cases,
479
Appendix B
GM Control Systems on Isuzu and Isuzu-built Geo
check and verify all circuits and parts involved in data communication before condemning the
ECM.
i
NOTE:
You may need a wiring diagram for the specific test vehicle along with troubleshooting
procedures from the manufacturer for some of the following checks.
Check the ALDL connector with a digital voltmeter (Figure B-4) if the CHECK ENGINE lamp
does not flash code 12, or if it does but the scan tool does not receive data.
A
B
C
A
B
F
E
D
C
B
A
G
H
J
K
L
M
C
Figure B-4 Isuzu and Isuzu-built Geo ALDL 3-pin and 12-pin connectors
A—CHECK ENGINE lamp/data transmission
B—Test or diagnostic enable
C—Ground
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To check ground continuity:
1. Connect the voltmeter positive (+) lead to ALDL pin A on the 12-pin connector, or to
pin C on the 3-pin connector.
2. Connect the negative (–) lead to the negative battery terminal. Use jumper wires as
needed.
i
NOTE:
Do not connect to a body or chassis ground; go directly to the negative battery terminal.
3. Measure voltage drop with the ignition switched on.
Voltage drop across the ground terminal should be 0.1 V or less. An open or high
resistance ground prevents the ECM from entering the diagnostic mode.
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To test for an open ground at ALDL pin A (or C):
1. Turn the ignition on and jumper pin B to pin A in the 12-pin ALDL connector, or pin A to
pin C on the 3-pin connector.
2. Connect the voltmeter positive lead to the jumper and the negative lead to a known good
ground; connect directly to the negative battery terminal if possible.
– The meter should read 50 millivolts (0.050 V) or less for a good ground (Figure B-5 on
page 481).
– Higher readings indicate a high-resistance ALDL ground connection.
– If the meter reads 5 V, the ALDL ground connection is open.
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F
E
D
C
B
A
G
H
J
K
L
M
0.050V
B
A B C
A
C
Figure B-5 Ground continuity for the ALDL connector
A—Voltmeter
B—Jump pin B to pin A
C—Jump pin A to pin C
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To check voltage on the test terminal:
• Connect the voltmeter positive lead to pin B of the 12-pin ALDL connector, or to pin A of
the 3-pin connector, and the negative lead to the ALDL ground pin or a good ground.
With the ignition on, voltage should be 5 V. If the test terminal (pin B or pin A) circuit is
open, a 160-baud ECM cannot switch into diagnostic mode.
z
To check voltage on pin B of the 3-pin connector (CHECK ENGINE lamp):
• Connect the voltmeter positive lead to ALDL pin B and the negative lead to the ground pin
or a known good ground.
With the ignition on and the engine off, voltage on pin B should be less than 1 V (0.7 to
0.8 V) when the lamp is on. When the lamp goes off with the engine running, meter
readings should rise to battery voltage. If the circuit to pin B is open, the ECM cannot
transmit data to the scan tool.
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To check voltage on pin E of the 12-pin connector:
• Connect the positive voltmeter lead to connector pin E and the negative lead to either pin
A or a good ground.
With the ignition on, voltage should be 5 V or fluctuating between 3.5 and 5.0 V. If the
circuit is open, the ECM cannot transmit data to the scan tool.
481
Appendix B
482
GM Control Systems on Isuzu and Isuzu-built Geo