Jeep XJ. Manual — part 642
Symptom:
P1597-SPEED CONTROL SWITCH ALWAYS LOW - DIESEL
When Monitored and Set Condition:
P1597-SPEED CONTROL SWITCH ALWAYS LOW - DIESEL
When Monitored:
With the ignition on and battery voltage above 10.4 volts.
Set Condition:
The PCM detects voltage below 0.39 volt on the S/C switch signal circuit
for at least 2 minutes.
POSSIBLE CAUSES
INTERMITTENT CONDITION
SPEED CONTROL ON/OFF SWITCH
SPEED CONTROL RESUME/ACCEL SWITCH
SPEED CONTROL SWITCH CONTROL CIRCUIT SHORTED TO SENSOR GROUND
SPEED CONTROL SWITCH CONTROL CIRCUIT SHORTED TO GROUND
PCM
TEST
ACTION
APPLICABILITY
1
Turn the ignition on.
With the DRBIII
t, read the Speed Control voltage.
Is the Speed Control voltage below 1.0 volts?
All
Yes
→
No
→
2
Turn the ignition on.
With the DRBIII
t, monitor the Speed Control Switch voltage.
Disconnect the Speed Control On/Off Switch harness connector.
Did the volt change to above 4.7 volts?
All
Yes
→
Replace the Speed Control On/Off Switch.
Perform SPEED CONTROL VERIFICATION - VER-4.
No
→
3
Turn the ignition on.
With the DRBIII
t, monitor the Speed Control Switch voltage.
Disconnect the Speed Control Resume/Accel Switch harness connector.
Did the volt change to above 4.7 volts?
All
Yes
→
Replace the Speed Control Resume/Accel Switch.
Perform SPEED CONTROL VERIFICATION - VER-4.
No
→
220
SPEED CONTROL
TEST
ACTION
APPLICABILITY
4
Turn the ignition off.
Disconnect the Speed Control On/Off Switch harness connector.
Disconnect the Speed Control Resume/Accel Switch harness connector.
Disconnect the PCM harness connector.
Measure the resistance between the Speed Control Switch circuit and the Sensor
ground circuit in the PCM harness connector.
Is the resistance below 5.0 ohms?
All
Yes
→
Repair the Speed Control Switch Signal circuit shorted to Sensor
ground circuit.
Perform SPEED CONTROL VERIFICATION - VER-4.
No
→
5
Turn the ignition off.
Disconnect the Speed Control On/Off Switch harness connector.
Disconnect the Speed Control Resume/Accel Switch harness connector.
Disconnect the PCM harness connector.
Measure the resistance of the Speed Control Switch circuit in PCM harness
connector to ground.
Is the resistance below 5.0 ohms?
All
Yes
→
Repair the Speed Control Switch Signal circuit shorted to ground.
Perform SPEED CONTROL VERIFICATION - VER-4.
No
→
6
If there are no possible causes remaining, view repair.
All
Repair
Replace the Powertrain Control Module in accordance with the
Service Information.
Perform SPEED CONTROL VERIFICATION - VER-4.
7
WARNING: KEEP CLEAR OF THE ENGINE’S MOVING PARTS.
NOTE: The conditions that set the DTC are not present at this time. The
following list may help in identifying the intermittent condition.
With the engine running at normal operating temperature, monitor the DRB
parameters related to the DTC while wiggling the wiring harness. Look for param-
eter values to change and/or a DTC to set.
Review the DTC When Monitored and Set Conditions. If possible, try to duplicate the
conditions under which the DTC was set.
Refer to any Technical Service Bulletins (TSB) that may apply.
Visually inspect the related wiring harness. Look for any chafed, pierced, pinched, or
partially broken wires.
Visually inspect the related wiring harness connectors. Look for broken, bent, pushed
out, or corroded terminals.
Were any of the above conditions present?
All
Yes
→
Repair as necessary
Perform SPEED CONTROL VERIFICATION - VER-4.
No
→
Test Complete.
221
SPEED CONTROL
P1597-SPEED CONTROL SWITCH ALWAYS LOW - DIESEL —
Continued
Symptom:
*CHECKING THE SPEED CONTROL OPERATION
POSSIBLE CAUSES
BRAKE LAMP SWITCH - PRIMARY CIRCUIT
BRAKE LAMP SWITCH - SECONDARY CKT
CHECKING BRAKE LAMP SWITCH ADJUSTMENT
CHECKING THE S/C LAMP OPERATION
CHECKING THE VEHICLE SPEED SIGNAL
ECM - BRAKE SWITCH SIGNAL
ECM - PRIMARY BRAKE SWITCH CIRCUIT
ECM - S/C LAMP CONTROL
ECM - S/C SIGNAL
ECM - SPEED CONTROL
FUSED B+ CIRCUIT OPEN
GROUND CIRCUIT OPEN
PCM - S/C LAMP CONTROL
PRIMARY BRAKE SWITCH SIGNAL CIRCUIT OPEN
PRIMARY BRAKE SWITCH SIGNAL CIRCUIT SHORTED TO GROUND
S/C LAMP SIGNAL OPEN
S/C LAMP SIGNAL SHORTED TO GROUND
S/C LAMP SIGNAL SHORTED TO VOLTAGE
S/C SWITCH SIGNAL CIRCUIT OPEN
S/C SWITCH SIGNAL CIRCUIT SHORTED TO GROUND
S/C SWITCHES
SECONDARY BRAKE SWITCH SIGNAL CIRCUIT OPEN
SECONDARY BRAKE SWITCH SIGNAL CIRCUIT SHORTED TO GROUND
SENSOR GROUND CIRCUIT OPEN
INTERMITTENT CONDITION
222
SPEED CONTROL
TEST
ACTION
APPLICABILITY
1
Start the engine.
With the DRB, select Engine, Bosch Controller then Sensor Display.
Observe the cruise switch volts on the DRB while pressing and holding each cruise
button separately.
NOTE: Pressing each cruise button should result in the following voltages:
ON/OFF 0.55 - 1.15v, SET 3.15 - 3.6v, RESUME/ACCEL 3.9 - 4.15v, CANCEL 1.55
- 2.05v, COAST 2.5 - 3.0v, No Button Pressed 4.4 - 4.7v
Does each switch provide the correct voltage?
All
Yes
→
No
→
2
Turn the ignition on.
With the DRB, select Engine, Bosch and Inputs/Outputs.
Observe the Brake Switch input while pressing and releasing the brake pedal several
times.
Does the DRB indicate the correct change of state from Released to Pressed?
All
Yes
→
No
→
3
Turn the ignition on.
With the DRB, select Engine, Bosch and Inputs/Outputs.
Observe the Brake Switch input while pressing and releasing the brake pedal several
times.
Does the DRB indicate the correct change of state from Released to Pressed?
All
Yes
→
No
→
4
With the DRB, select Engine, then Bosch Controller and monitor the Vehicle Speed
Signal while test driving the vehicle.
Does the DRB display accurate vehicle speed?
All
Yes
→
No
→
Refer to symptom list for problems related to Vehicle Speed
Sensor Signal.
Perform SPEED CONTROL VERIFICATION - VER-4.
5
Drive the vehicle and generate a vehicle speed above 55 Km/h (35 mph).
Attempt to set the speed control.
Did vehicle speed control maintain set vehicle speed?
All
Yes
→
No
→
6
Drive the vehicle and generate a vehicle speed above 55 Km/h (35 mph).
Set the speed control and observe the Speed Control Lamp.
Does the Speed Control Lamp illuminate when speed control is on?
All
Yes
→
Test Complete.
No
→
223
SPEED CONTROL
*CHECKING THE SPEED CONTROL OPERATION —
Continued
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