Page 152 of 5267

5.(F855) PRIMARY 5-VOLT SUPPLY SHORTED TO BATTERY VOLTAGE
Turn the ignition off.
Disconnect the C2 PCM harness connector.
Disconnect all the Sensors that share the (F855) Primary 5-volt Supply
circuit.
Ignition on, engine not running.
Measure the voltage on the (F855) Primary 5-volt Supply circuit in the
CKP Sensor harness connector.
Is the voltage above 0 volts?
Ye s>>
Repair the short to battery voltage in the (F855) Primary
5-volt Supply circuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to
9 - ENGINE - STANDARD PROCEDURE)
No>>
Go To 6
6.(F855) PRIMARY 5-VOLT SUPPLY CIRCUIT OPEN
Turn the ignition off.
Reconnect all the sensors that were disconnected in the previous step
except for the CKP Sensor harness connector.
CAUTION: Do not probe the PCM harness connectors. Probing the
PCM harness connectors will damage the PCM terminals resulting
in poor terminal to pin connection. Install Miller Special Tool #8815
to perform diagnosis.
Measure the resistance in the (F855) Primary 5-volt Supply circuit from
the Sensor harness connector to the appropriate terminal of special tool
#8815.
It may be necessary to perform this test from every sensor that uses
the (F855) Primary 5-volt Supply circuit.
Is the resistance below 5.0 ohms?
Ye s>>
Go To 7
No>>
Repair the open in the (F855) Primary 5-volt Supply circuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to
9 - ENGINE - STANDARD PROCEDURE)
Page 154 of 5267
P1628-SENSOR REFERENCE VOLTAGE 2 CIRCUIT ERRATIC
For a complete wiring diagramRefer to Section 8W.
Page 155 of 5267

When Monitored:
Ignition on.
Set Condition:
When the PCM recognizes the Auxiliary 5-volt Supply circuit voltage is varying too much too quickly. One Trip
Fault. ETC light is flashing.
Possible Causes
(F856) AUXILIARY 5-VOLT SUPPLY CIRCUIT SHORTED TO GROUND
(F856) AUXILIARY 5-VOLT SUPPLY CIRCUIT SHORTED TO BATTERY VOLTAGE
(F856) AUXILIARY 5-VOLT SUPPLY CIRCUIT OPEN
5-VOLT SENSOR
PCM
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE -
DIAGNOSIS AND TESTING).
Diagnostic Test
1.ACTIVE DTC
Ignition on, engine not running.
With a scan tool, read DTCs.
Is the DTC active at this time?
Ye s>>
Go To 2
No>>
Refer to the INTERMITTENT CONDITION Diagnostic Procedure.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
2.(F856) AUXILIARY 5-VOLT SUPPLY CIRCUIT SHORTED TO GROUND
Turn the ignition off.
Disconnect the C1 PCM harness connector.
Disconnect all the Sensors that share the (F856) Auxiliary 5-volt Supply
circuit.
NOTE: This code can be caused by the improper installation of
after market accessories that may be causing excessive noise on
the (F856) 5-volt Supply circuit.
Measure the resistance between ground and the (F856) Auxiliary 5-volt
Supply circuit at the CMP Sensor harness connector.
Istheresistancebelow100ohms?
Ye s>>
Repair the short to ground in the (F856) Auxiliary 5-volt
Supply circuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to
9 - ENGINE - STANDARD PROCEDURE)
No>>
Go To 3
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3.SENSOR SHORTED TO GROUND
Connect the C1 PCM harness connector and all the previously discon-
nected Sensor except for the CMP Sensor harness connector.
Ignition on, engine not running.
Measure the voltage on the (F856) Auxiliary 5-volt Supply circuit in the
CMP Sensor harness connector.
CAUTION: You must Turn the Ignition OFF when disconnecting any
of the Sensor harness connectors and Turn the Ignition On to
check the voltage readings.
While monitoring the voltage, disconnect each Sensor harness connec-
tor that shares the (F856) Auxiliary 5-volt Supply circuit, one at a time.
Does the voltage increase above 4.5 volts when disconnecting
any of the Sensor harness connectors?
Ye s>>
Replace the Sensor that causes the (F856) Auxiliary 5-volt
Supply circuit voltage to increase when disconnected.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to
9 - ENGINE - STANDARD PROCEDURE)
No>>
Go To 4
4.5-VOLT SENSOR
Turn the ignition off.
Connect all the previously disconnected Sensors except for the CMP
Sensor harness connector.
Ignition on, engine not running.
Measure the voltage on the (F856) Auxiliary 5-volt Supply circuit in the
CMP Sensor harness connector.
Is the voltage below 4.5 volts?
Ye s>>
Go To 5
No>>
Replace the Cam Position Sensor.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to
9 - ENGINE - STANDARD PROCEDURE)
Page 157 of 5267

5.(F856) AUXILIARY 5-VOLT SUPPLY CIRCUIT SHORTED TO BATTERY VOLTAGE
Turn the ignition off.
Disconnect the C1 PCM harness connector.
Disconnect all the Sensors that share the (F856) Auxiliary 5-volt Supply
circuit.
Ignition on, engine not running.
Measure the voltage on the (F856) Auxiliary 5-volt Supply circuit at the
CMP Sensor harness connector.
Is the voltage above 0 volts?
Ye s>>
Repair the short to battery voltage in the (F856) Auxiliary
5-volt Supply circuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to
9 - ENGINE - STANDARD PROCEDURE)
No>>
Go To 6
6.(F856) AUXILIARY 5-VOLT SUPPLY CIRCUIT OPEN
Turn the ignition off.
Reconnect all the sensors that were disconnected in the previous step
except the CMP Sensor harness connector.
CAUTION: Do not probe the PCM harness connectors. Probing the
PCM harness connectors will damage the PCM terminals resulting
in poor terminal to pin connection. Install Miller Special Tool #8815
to perform diagnosis.
Measure the resistance in the (F856) Auxiliary 5-volt Supply circuit from
the Sensor harness connector to the appropriate terminal of special tool
#8815.
It may be necessary to perform this test from every sensor that uses
the (F856) Auxiliary 5-volt Supply circuit.
Is the resistance below 5.0 ohms?
Ye s>>
Go To 7
No>>
Repair the open in the (F856) Auxiliary 5-volt Supply circuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to
9 - ENGINE - STANDARD PROCEDURE)
7.PCM
NOTE: Before continuing, check the PCM harness connector terminals for corrosion, damage, or terminal
push out. Repair as necessary.
Using the schematics as a guide, inspect the wire harness and connectors. Pay particular attention to all Power and
Ground circuits.
Were there any problems found?
Ye s>>
Repair as necessary.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No>>
Replace and program the Powertrain Control Module per Service Information.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
Page 162 of 5267
P1897-LEVEL 1 RPM BUS UNLOCK
For a complete wiring diagramRefer to Section 8W.
When Monitored:
Engine running.
Set Condition:
When the PCM recognizes an internal failure to communicate with the FCM or the CMP and CKP Sensor
count periods are too short. One trip fault. ETC light is flashing.
Possible Causes
PCM
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE -
DIAGNOSIS AND TESTING).
Diagnostic Test
1.PCM
NOTE: Diagnose any CMP or CKP Sensor faults before continuing. Check for intermittent loose CMP or CKP
connections.
The Powertrain Control Module is reporting internal errors, view repair to continue.
Repair
Replace and program the Powertrain Control Module per Service Information.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
Page 165 of 5267

Theory of Operation
This DTC sets when an unexpected high intake manifold air flow condition exists that can lead to increased engine
speed and puts the NGC into a High Air flow Protection limiting mode. The High Air flow Protection feature includes
RPM limits for when a Throttle and/or MAP sensor limp-in fault is present.
When Monitored:
During all drive modes
Set Condition:
If vacuum drops below 1.5
Hg with engine RPM greater than 2000 RPM and closed throttle. One Trip Fault.
Three good trips to turn off the MIL.
Possible Causes
VACUUM LEAK
RESISTANCE IN THE (F856) 5-VOLT SUPPLY CIRCUIT
(F856) 5-VOLT SUPPLY CIRCUIT SHORTED TO GROUND
RESISTANCE IN THE (K1) MAP SIGNAL CIRCUIT
(K1) MAP SIGNAL CIRCUIT SHORTED TO GROUND
RESISTANCE IN THE (F855) 5-VOLT SUPPLY CIRCUIT
(F855) 5-VOLT SUPPLY CIRCUIT SHORTED TO GROUND
RESISTANCE IN THE (K22) TP SENSOR NO.1 SIGNAL CIRCUIT
(K22) TP SENSOR NO.1 SIGNAL CIRCUIT SHORTED TO GROUND
RESISTANCE IN THE (K900) SENSOR GROUND CIRCUIT
MAP SENSOR
THROTTLE POSITION SENSOR
PCM
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE -
DIAGNOSIS AND TESTING).
Diagnostic Test
1.ACTIVE DTC
NOTE: Diagnose any TP Sensor or MAP Sensor component DTCs before continuing.
NOTE: If the P0501 - No Vehicle Speed Signal is set long with this DTC, refer to the P0501 diagnostics
before continuing.
NOTE: The throttle plate and linkage should be free from binding and carbonbuild up.
NOTE: Make sure the throttle plate is at the idle position.
Ignition on, engine not running.
With a scan tool, read DTCs.
Is the DTC active at this time?
Ye s>>
Go To 2
No>>
Refer to the INTERMITTENT CONDITION Diagnostic Procedure.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
Page 166 of 5267

2.VACUUM LEAK
NOTE: This code is enabled on engines with a plastic intake manifold and is intended to shut down the
engine if a large crack occurs.
NOTE: A large vacuum leak is most likely the cause of this DTC.
Inspect the Intake Manifold for leaks and cracks.
Inspect the Power Brake Booster for any vacuum leaks.
Inspect the PCV system for proper operation and vacuum leaks.
Inspect the throttle plate to see if it is bent and will close entirely, if itis bent it may need to be replaced.
Inspect the MAP Sensor for proper installation.
Verify the engine is free from any mechanical failures.
Were any vacuum leaks found?
Ye s>>
Repair the vacuum leak as necessary.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No>>
Go To 3
3.MAP SENSOR OPERATION
Start the engine.
With a scan tool, monitor the MAP Sensor voltage.
Snap the throttle.
Does the MAP Sensor voltage vary from below 2.0 volts at idle to above 3.5 volts at wide open throt-
tle?
Ye s>>
Go To 4
No>>
Go To 11
4.TP SENSOR OPERATION
Ignition on, engine not running.
With a scan tool, monitor the TP Sensor voltage while slowly pressing the throttle pedal from closed to wide open
throttle.
Does voltage start at approximately 0.8 of a volt and go above 3.5 volts witha smooth transition?
Ye s>>
Refer to the INTERMITTENT CONDITION Diagnostic Procedure.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No>>
Go To 5