
Symptom List:
P0641-SENSOR REFERENCE VOLTAGE A CKT VOLTAGE TOO LOW
P0651-SENSOR REFERENCE VOLTAGE B CKT VOLTAGE TOO LOW
Test Note: All symptoms listed above are diagnosed using the same tests.
The title for the tests will be P0641-SENSOR REFERENCE
VOLTAGE A CKT VOLTAGE TOO LOW.
When Monitored and Set Condition:
P0641-SENSOR REFERENCE VOLTAGE A CKT VOLTAGE TOO LOW
When Monitored: With the ignition on.
Set Condition: The ECM detects an open or short to ground on the Sensor Reference
Voltage A circuit.
P0651-SENSOR REFERENCE VOLTAGE B CKT VOLTAGE TOO LOW
When Monitored: With the ignition on.
Set Condition: The ECM detects an open or short to ground on the Sensor Reference
Voltage B circuit.
POSSIBLE CAUSES
INTERMITTENT CONDITION
MAF, OIL PRESS, BOOST PRESS, A/C PRESS, APP OR FUEL PRESS SENSOR SHORT TO
GROUND
SENSOR REFERENCE VOLTAGE OR 5-VOLT SUPPLY CIRCUIT SHORTED TO GROUND
SENSOR REFERENCE VOLTAGE OR 5-VOLT SUPPLY CIRCUIT SHORTED TO SENSOR
GROUND
5-VOLT SUPPLY CIRCUIT SHORTED TO GROUND
5-VOLT SUPPLY CIRCUIT SHORTED TO SENSOR GROUND
ENGINE CONTROL MODULE
TEST ACTION APPLICABILITY
1 Turn the ignition on.
With the DRB, erase ECM DTCs.
Monitor the DRB for ECM DTCs.
Did this DTC reset?All
Ye s®Go To 2
No®Go To 8
136
DRIVEABILITY - DIESEL

TEST ACTION APPLICABILITY
2 Turn the ignition on.
With the DRBIIItin Sensors, monitor the MAF, Oil Pressure, Boost Pressure, A/C
Pressure, APP and Fuel Pressure Sensors.
NOTE: If any sensor reading is above zero before disconnecting, it is not
necessary to disconnect it for this test.
One at a time while monitoring the DRB sensor readings, disconnect the MAF, Oil
Pressure, Boost Pressure, A/C Pressure, APP and Fuel Pressure Sensor harness
connectors.
NOTE: If one of the sensors is shorted to ground internally, disconnecting it
will cause the voltage reading on the DRB to rise for all sensors.
Did the DRB sensor voltage readings rise?All
Ye s®Replace the Sensor that, when disconnected, caused the DRB
sensor readings to rise.
Perform ROAD TEST VERIFICATION - VER-2.
No®Go To 3
3 Turn the ignition off.
Disconnect the ECM harness connectors.
Disconnect the MAF Sensor harness connector.
Measure the resistance between ground and the Sensor Reference Voltage A circuit,
then ground and the MAF Sensor 5-Volt Supply circuit.
Disconnect the Boost Pressure Sensor, Engine Oil Pressure Sensor, and A/C Pressure
Sensor harness connectors.
Measure the resistance between ground and the Sensor Reference Voltage B circuit,
then ground and the 5-Volt Supply circuits to the Boost Pressure Sensor, A/C
Pressure Sensor and Engine Oil Pressure Sensor.
Is the resistance above 100k ohms for all of the measurements?All
Ye s®Go To 4
No®Repair the Sensor Reference Voltage or 5-Volt Supply circuit that
measured less than 100k ohms for a short to ground.
Perform ROAD TEST VERIFICATION - VER-2.
4 Turn the ignition off.
Disconnect the ECM harness connectors.
Disconnect the MAF Sensor harness connector.
Measure the resistance between the Sensor Reference Voltage A circuit and the MAF
Sensor Ground circuit.
Disconnect the Boost Pressure Sensor, Engine Oil Pressure Sensor, and A/C Pressure
Sensor harness connectors.
Measure the resistance between the Sensor Reference Voltage B circuit and the Boost
Pressure Sensor Ground circuit, then the A/C Pressure Sensor Ground circuit, and
finally the Engine Oil Pressure Sensor Ground circuit.
Is the resistance above 100k ohms for all measurements?All
Ye s®Go To 5
No®Repair the Sensor Reference Voltage or 5-Volt Supply circuit that
measured less than 100k ohms for a short to the Sensor Ground
circuit.
Perform ROAD TEST VERIFICATION - VER-2.
137
DRIVEABILITY - DIESEL
P0641-SENSOR REFERENCE VOLTAGE A CKT VOLTAGE TOO LOW Ð
Continued

Verification Tests
CHARGING VERIFICATION - VER-3 APPLICABILITY
1. Inspect the vehicle to ensure that all engine components are properly installed and
connected. Reassemble and reconnect components as necessary.
2. If the PCM has been replaced, perform step 3. Otherwise, continue with step 4.
3. If the vehicle is equipped with a factory theft alarm, start the engine at least 20 times in
order to be able to activate the alarm system when desired.
4. With the DRB, erase all diagnostic trouble codes (DTCs).
5. Start the engine.
6. Raise the engine speed to 2000 RPM for at least 30 seconds.
7. Allow the engine to idle.
8. Turn the ignition off for 20 seconds.
9. Turn the ignition on.
10. With the DRB, read ECM and PCM DTCs.
11. If this DTC has reset, or another DTC has set, look for any Technical Service Bulletins
(TSBs) that may relate to this condition. Return to the Symptom List if necessary.
12. If the charging system is functioning correctly and there are no DTCs, the repair is now
complete.
Are any DTCs or symptoms remaining?All
Ye s®Repair is not complete, refer to appropriate symptom.
No®Repair is complete.
NO START VERIFICATION - VER-1 APPLICABILITY
1. NOTE: IMPORTANT! If the Engine Control Module, Sentry Key Immobilizer
Module or Powertrain Control Module have been replaced, ensure the programming
procedures for these modules have been performed in accordance with the Service
Information.
2. Inspect the vehicle to ensure that all engine components are properly installed and
connected. Reassemble and reconnect components as necessary.
3. Inspect the engine oil for contamination. If it is contaminated, change the oil and filter.
4. With the DRB, erase all diagnostic trouble codes (DTCs).
5. Turn the ignition off for at least 10 seconds.
6. Attempt to start the engine.
7. If the engine is unable to start, look for any Technical Service Bulletins (TSBs) that may
relate to this condition. Return to the Symptom List if necessary.
8. If the engine starts and continues to run, the repair is now complete.
Are any DTCs or symptoms remaining?All
Ye s®Repair is not complete, refer to appropriate symptom.
No®Repair is complete.
223
VERIFICATION TESTS

ENGINE CONTROL MODULE C1 (DIESEL) - BLACK 81 WAYCAV CIRCUIT FUNCTION
1 Z130 14BK/BR GROUND
2 Z131 14BK/DG GROUND
3 K20 14BR/GY GENERATOR FIELD CONTROL
4 K342 14BR/WT ECM/PCM RELAY OUTPUT
5 K342 14BR/WT ECM/PCM RELAY OUTPUT
6- -
7 D25 20WT/VT PCI BUS
8 K944 20BK/GY CAMSHAFT POSITION SENSOR SHIELD GROUND
9 K44 20DB/GY CAMSHAFT POSITION SENSOR SIGNAL
10 - -
11 K37 20DB/YL BOOST PRESSURE SENSOR SIGNAL
12 K55 20DB/OR MASS AIR FLOW SENSOR SIGNAL
13 K78 20GY FUEL PRESSURE SENSOR SIGNAL
14 - -
15 K22 20OR/DB ACCELERATOR PEDAL POSITION SENSOR SIGNAL
16 K80 20DB/TN FUEL PRESSURE SENSOR GROUND
17 - -
18 - -
19 N1 20DB/OR FUEL HEATER RELAY OUTPUT
20 Z138 20BK/OR GROUND
21 K900 20DB/DG SENSOR GROUND
22 F202 20PK/GY IGNITION SWITCH OUTPUT (RUN-START)
23 F851 20LB/PK SENSOR REFERENCE VOLTAGE B
24 K3 20BR/OR CRANKSHAFT POSITION SENSOR SIGNAL NO. 1
25 - -
26 - -
27 - -
28 - -
29 - -
30 G6 20VT/GY ENGINE OIL PRESSURE SENSOR SIGNAL
31 F853 20LG/PK WATER IN FUEL SENSOR SIGNAL
32 K25 20BR/TN BATTERY TEMPERATURE SENSOR SIGNAL
33 - -
34 K167 20BR/YL ACCELERATOR PEDAL POSITION SENSOR GROUND
35 K853 20DB/BR ACCELERATOR PEDAL POSITION SENSOR 5 VOLT SUPPLY
36 C18 20LB/BR A/C PRESSURE SENSOR SIGNAL
37 K89 20DB/WT ENGINE OIL TEMPERATURE SENSOR SIGNAL
38 V37 20VT/TN SPEED CONTROL SWITCH SIGNAL
39 - -
40 K2 20TN/BK ENGINE COOLANT TEMPERATURE SENSOR SIGNAL
41 K21 20DB/LG INTAKE AIR TEMPERATURE SENSOR SIGNAL
42 Z122 18WT GROUND (DRAIN)
43 K24 20BR/LB CRANKSHAFT POSITION SENSOR SIGNAL NO. 2
44 - -
45 - -
46 - -
47 L50 20WT/TN PRIMARY BRAKE SWITCH SIGNAL
48 B29 20DG/WT SECONDARY BRAKE SWITCH SIGNAL
49 T751 20YL IGNITION SWITCH OUTPUT (START)
50 F855 20PK/YL SENSOR REFERENCE VOLTAGE A
C
O
N
N
E
C
T
O
R
P
I
N
O
U
T
S
234
CONNECTOR PINOUTS

ENGINE CONTROL MODULE C1 (DIESEL) - BLACK 81 WAYCAV CIRCUIT FUNCTION
51 - -
52 K121 20DB BOOST PRESSURE SENSOR GROUND
53 - -
54 K957 20BK/OR MASS AIR FLOW SENSOR GROUND
55 N7 20DB/OR VEHICLE SPEED SENSOR SIGNAL
56 C918 20BK/LB A/C PRESSURE SENSOR GROUND
57 - -
58 K4 20BK/LB LOW IDLE POSITION SWITCH GROUND
59 - -
60 K9 20LB FUEL PRESSURE SENSOR 5 VOLT SUPPLY
61 K51 20BR/WT ECM/PCM RELAY CONTROL
62 - -
63 D21 20WT/BR SCI TRANSMIT
64 K151 20WT LOW IDLE POSITION SWITCH SENSE
65 - -
66 K936 20BR/YL ENGINE OIL PRESSURE SENSOR GROUND
67 - -
68 - -
69 C13 20LB/OR A/C COMPRESSOR CLUTCH RELAY CONTROL
70 N210 20DB/DG LOW SPEED RADIATOR FAN RELAY CONTROL
71 - -
72 N21 20DB/TN LIFT PUMP RELAY CONTROL
73 - -
74 T752 20DG/OR ENGINE STARTER MOTOR RELAY CONTROL
75 - -
76 - -
77 K152 20DB/WT GLOW PLUG RELAY CONTROL
78 N122 20DB/YL HIGH SPEED RADIATOR FAN DUAL RELAY CONTROL
79 - -
80 K87 20BR FUEL PRESSURE SOLENOID CONTROL
81 K87 20BR FUEL PRESSURE SOLENOID CONTROL
C
O
N
N
E
C
T
O
R
P
I
N
O
U
T
S
235
CONNECTOR PINOUTS

ENGINE OIL PRESSURE SENSOR (DIESEL) - BLACK 3 WAYCAV CIRCUIT FUNCTION
1 F855 20PK/YL SENSOR REFERENCE VOLTAGE A
2 G6 20VT/GY ENGINE OIL PRESSURE SENSOR SIGNAL
3 K936 20BR/YL ENGINE OIL PRESSURE SENSOR GROUND
ENGINE OIL TEMPERATURE SENSOR (DIESEL) - BLACK 2 WAYCAV CIRCUIT FUNCTION
1 K89 20DB/WT ENGINE OIL TEMPERATURE SENSOR SIGNAL
2 K900 20DB/OR SENSOR GROUND
FUEL HEATER (DIESEL) - BLACK 2 WAYCAV CIRCUIT FUNCTION
1 N1 16RD FUEL HEATER RELAY OUTPUT
2 Z201 18RD GROUND
FUEL INJECTOR NO. 1 (DIESEL) - BLACK 2 WAYCAV CIRCUIT FUNCTION
1 K111 14DB/LB COMMON INJECTOR DRIVER
2 K11 14WT/DB FUEL INJECTOR NO. 1 CONTROL
FUEL INJECTOR NO. 2 (DIESEL) - BLACK 2 WAYCAV CIRCUIT FUNCTION
1 K111 14DB/LB COMMON INJECTOR DRIVER
2 K12 14TN FUEL INJECTOR NO. 2 CONTROL
C
O
N
N
E
C
T
O
R
P
I
N
O
U
T
S
237
CONNECTOR PINOUTS

FASTENER IDENTIFICATION
DESCRIPTION
The SAE bolt strength grades range from grade 2
to grade 8. The higher the grade number, the greater
the bolt strength. Identification is determined by the
line marks on the top of each bolt head. The actual
bolt strength grade corresponds to the number of line
marks plus 2. The most commonly used metric bolt
strength classes are 9.8 and 10.9. The metric
strength class identification number is imprinted on
the head of the bolt. The higher the class number,
the greater the bolt strength. Some metric nuts are
imprinted with a single-digit strength class on the
nut face. Refer to the Fastener Identification and
Fastener Strength Charts.
FASTENER USAGE
DESCRIPTION - FASTENER USAGE
WARNING: USE OF AN INCORRECT FASTENER
MAY RESULT IN COMPONENT DAMAGE OR PER-
SONAL INJURY.
Figure art, specifications and torque references in
this Service Manual are identified in metric and SAE
format.
During any maintenance or repair procedures, it is
important to salvage all fasteners (nuts, bolts, etc.)
for reassembly. If the fastener is not salvageable, a
fastener of equivalent specification must be used.
International Symbols
1 High Beam 13 Rear Window Washer
2 Fog Lamps 14 Fuel
3 Headlamp, Parking Lamps, Panel Lamps 15 Engine Coolant Temperature
4 Turn Warning 16 Battery Charging Condition
5 Hazard Warning 17 Engine Oil
6 Windshield Washer 18 Seat Belt
7 Windshield Wiper 19 Brake Failure
8 Windshield Wiper and Washer 20 Parking Brake
9 Windscreen Demisting and Defrosting 21 Front Hood
10 Ventilating Fan 22 Rear hood (Decklid)
11 Rear Window Defogger 23 Horn
12 Rear Window Wiper 24 Lighter
RSINTRODUCTION5
INTERNATIONAL SYMBOLS (Continued)

FASTENER USAGE
DESCRIPTION
WARNING: USE OF AN INCORRECT FASTENER
MAY RESULT IN COMPONENT DAMAGE OR PER-
SONAL INJURY.
Figure art, specifications and torque references in
this Service Manual are identified in metric and SAE
format.
During any maintenance or repair procedures, it is
important to salvage all fasteners (nuts, bolts, etc.)
for reassembly. If the fastener is not salvageable, a
fastener of equivalent specification must be used.
THREADED HOLE REPAIR
DESCRIPTION
Most stripped threaded holes can be repaired using
a Helicoilt. Follow the vehicle or Helicoiltrecommen-
dations for application and repair procedures.
INTERNATIONAL VEHICLE
CONTROL & DISPLAY
SYMBOLS
DESCRIPTION
The graphic symbols illustrated in the following
International Control and Display Symbols Chart
(Fig. 4) are used to identify various instrument con-
trols. The symbols correspond to the controls and dis-
plays that are located on the instrument panel.
Fig. 4 INTERNATIONAL CONTROL AND DISPLAY SYMBOLS
1 High Beam 13 Rear Window Washer
2 Fog Lamps 14 Fuel
3 Headlamp, Parking Lamps, Panel Lamps 15 Engine Coolant Temperature
4 Turn Warning 16 Battery Charging Condition
5 Hazard Warning 17 Engine Oil
6 Windshield Washer 18 Seat Belt
7 Windshield Wiper 19 Brake Failure
8 Windshield Wiper and Washer 20 Parking Brake
9 Windscreen Demisting and Defrosting 21 Front Hood
10 Ventilating Fan 22 Rear hood (Decklid)
11 Rear Window Defogger 23 Horn
12 Rear Window Wiper 24 Lighter
RGINTRODUCTION5a