Engine Controls - Tests W/codes - 6.5L: Diagnosis Chevrolet Tahoe I

SELF-DIAGNOSTIC SYSTEM

Note. SERVICE ENGINE SOON light, located on instrument cluster, is also referred to as the Malfunction Indicator Light (MIL).

The electronically-controlled transmission includes a self-diagnostic system which can determine input signal circuit malfunctions. Input signal circuits determine engine/transmission function control. When a malfunction occurs, PCM will illuminate the Malfunction Indicator Light (MIL). When malfunction is detected and MIL is illuminated, a corresponding Diagnostic Trouble Code (DTC) will be stored in PCM memory. To retrieve stored DTC(s), see ENTERING & EXITING DIAGNOSTIC MODE . Malfunctions are recorded as either hard failures or intermittent failures.

Preliminary Inspection

1. Check all vacuum hoses for correct routing, restrictions, cuts or other damage. Inspect difficult-to-see vacuum hoses beneath air cleaner assembly and other engine components.
2. Inspect all engine compartment wiring for proper connections. Also check wires for pinched or chafed spots, as well as contact with sharp edges or exhaust manifolds.
3. The preliminary inspection is very important and should be performed carefully and thoroughly, as it can often fix a problem without requiring further diagnosis.

Note. Begin all diagnosis with ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in the BASIC TESTING - 6.5L DIESEL article. After any systems repair, repeat ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK.

Diagnostic Procedure

1. Ensure all non-electronically controlled systems are operating properly. DO NOT proceed with testing unless all non-electronically controlled systems problems are repaired.
2. ALWAYS begin diagnosis with ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK to determine if transmission and PCM are working properly. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. If DTCs are displayed, determine if they are hard or intermittent trouble codes.
3. A hard code is present when working on vehicle, and problem persists. Hard codes will cause Malfunction Indicator Light (MIL) to come on. NOTE: SERVICE ENGINE SOON light, located on instrument cluster, is also referred to as the Malfunction Indicator Light (MIL).
4. An intermittent code does not reset itself and is NOT present while working on vehicle. Intermittent codes are often caused by loose connections. MIL will go out 10 seconds after fault goes away. For intermittent diagnostic procedures, see the TESTS W/O CODES article.

ENTERING & EXITING DIAGNOSTIC MODE

To enter diagnostic mode, the use of a scan tool is required. With ignition on and engine off, connect scan tool to Data Link Connector (DLC) located under left side of dash. (Scheme 13) The ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK will enter into a diagnostic system check. In this mode, PCM will display DTCs on scan tool. Refer to scan tool manufacturer's instructions. To exit diagnostic mode, turn ignition off and remove scan tool from DLC.

Scheme 13

CLEARING TROUBLE CODES

Note. To prevent PCM damage, ensure ignition switch is in OFF position when disconnecting or reconnecting power to PCM.

DTCs should be cleared after repairs have been completed. Also, some diagnostic procedures require DTCs to be cleared before performing diagnostic procedure.

To clear DTC(s), use scan tool. With ignition on and engine off, connect a scan tool to Data Link Connector (DLC) located behind left side of dash. (Scheme 13) Refer to scan tool manufacturer's instructions.

If no hard fault codes are present (only intermittent codes exist), proceed to the TESTS W/O CODES article for intermittent diagnostic procedures.

SPECIAL TOOLS (DIAGNOSTIC)

Special scan tools, plugged into the DLC, are used to read DTC(s) and check voltages in system on serial data line. Scan tools can save a great deal of time. Refer to scan tool manufacturer's instructions.

SCAN TOOL USAGE

Note. Before connecting scan tool, check diagnostic system and ensure accurate information is received by scan tool. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in the BASIC TESTING - 6.5L DIESEL article. If vehicle does not pass ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK, information received by scan tool may be invalid.

Scan tool is a specialized tool which can diagnose on-board computer control systems by providing almost instant access to circuit voltage information without crawling under dash or hood to backprobe sensors and connectors. Scan tools reduce diagnostic time by furnishing input data (voltage signals) which can be compared to specification parameters. See TYPICAL TECH 1 or 2 DATA VALUES table.

Scan tools also furnish information on output device (solenoids and motors) status. However, status parameters are only an indication output signals have been sent to devices by the PCM. They do not indicate whether devices respond properly to that signal. This must be verified at output device using a DVOM or a test light.

If DTC(s) are not present, a problem may still exist. Driveability-related problems with DTC(s) displayed occur about 20 percent of the time, while driveability problems without DTC(s) occur about 80 percent of the time. Out-of-calibration sensors WILL NOT set a DTC, but WILL cause driveability problems. Using a scan tool is the easiest method of checking sensor specifications and other data parameters. Scan tool is also useful in finding intermittent wiring problems by wiggling wiring harnesses and connections (key on, engine off) while observing data parameters. See TYPICAL TECH 1 OR 2 DATA VALUES table.

Note. Information obtained by scan tool is only as accurate as the scan tool itself. If erroneous voltage signals are suspected, verify scan tool information using a DVOM and wiring schematic.

TEST EQUIPMENT

A tachometer, test light, Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance, a vacuum gauge, and jumper wires are required to test and diagnose Diesel Electronic Control (DEC)/electronically-controlled transmission systems. A scan tool may also be used to access data parameters. Scan tool will supply a visual reading of most inputs, and some outputs, to PCM.

DIAGNOSTIC TROUBLE CODES

Note. Before clearing DTCs, record FREEZE FRAME and FAILURE RECORDS for reference during testing. Data will be erased when DTCs are cleared.

Note. If PCM is replaced, NEW PCM must be programmed using special equipment.

Note. In the following tests, illustrations are courtesy of General Motors Corp.

Diagnostic Procedures

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Turn ignition on, with engine off. Review and record scan tool Fail Records data. Operate vehicle within the Fail Records conditions. Using scan tool, monitor Specific DTC info for DTC P0101. If scan tool indicates that DTC P0101 failed this ignition cycle, go to next step. If scan tool does not indicate that DTC P0101 failed, see DIAGNOSTIC AIDS.
3. Check for plugged intake air duct, dirty air filter, intake manifold vacuum leaks or EGR leak. Repair or replace as necessary. After repairs, go to step 17). If no problems were found, go to next step.
4. Turn ignition on, with engine off. Ensure throttle is closed. Observe APP angle display on scan tool. APP angle should be zero percent. If APP angle is as specified or close to zero percent, go to next step. If APP angle is not as specified, see DTC P0121 for diagnosis.
5. Turn ignition off. Disconnect MAF sensor harness connector. Turn ignition on, with engine off. Using a DVOM, check voltage between MAF sensor harness connector terminal "A" (signal circuit) and chassis ground. DVOM should read 5 volts. If voltage reading is as specified, go to next step. If voltage reading is not as specified, go to step 7).
6. Connect a test light between MAF sensor harness connector terminals "C" (ignition feed circuit) and "B" (ground circuit). If test light illuminates, go to step 10). If test does not illuminate, go to step 9).
7. If voltage reading is less than 4.5 volts, go to step 11). If voltage reading is greater than 4.5 volts, go to next step.
8. Turn ignition off. Disconnect PCM harness connector. Turn ignition on, with engine off. Check voltage between MAF sensor harness connector terminal "A" and ground. If voltage reading is zero volts, go to step 15). If voltage reading is not zero volts, go to step 13).
9. Connect test light between MAF sensor harness connector terminal "C" and chassis ground. If test light illuminates, go to step 12). If test light does not illuminate, go to step 13).
10. Check for poor connection at MAF sensor. Repair or replace terminals as necessary. After repairs, go to step 17). If terminals are okay, go to step 15).
11. Check MAF signal circuit between PCM and MAF sensor for an open, short to ground, or short to MAF sensor ground circuit. Repair as necessary. After repairs, go to step 17). If circuits are okay, go to step 16).
12. Locate and repair open in ground circuit to MAF sensor. After repairs, go to step 17).
13. Locate and repair open in ignition feed circuit to MAF circuit. After repairs, go to step 17).
14. Locate and repair short to voltage in MAF sensor signal circuit. After repairs, go to step 17).
15. Replace MAF sensor. After replacing sensor, go to step 17).
16. Replace PCM. After replacing PCM, go to next step.
17. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC number that was set. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
18. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Diagnostic Aids

Check wiring harness for damage. If harness appears to be okay, observe scan tool while moving connectors and wiring harnesses related to the MAF sensor. A change in the display will indicate the location of fault.

Check for plugged intake air duct or dirty air filter. A wide-open throttle acceleration from a stop should cause the mass airflow displayed on scan tool to increase. If not, check for restrictions. If DTC P0101 cannot be duplicated, the information included in the Fail Records data can be useful in determining vehicle mileage since the DTC was last set and how often the DTC sets.

Mass Airflow System Diagram. Scheme 14

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Start engine. With engine at idle, monitor MAF display on scan tool. If MAF reading is less than 1280 Hz, go to step 4). If MAF reading is greater than 1280 Hz, go to next step.
3. Turn engine off. Turn ignition on, with engine off. Review and record Fail Records data on scan tool. Operate vehicle within the Fail Records conditions as noted. Using scan tool, monitor SPECIFIC DTC information for DTC P0102. If scan tool indicates that DTC P0102 failed in this ignition cycle, go to next step. If DTC P0102 did not fail in this ignition cycle, see DIAGNOSTIC AIDS.
4. Check for blocked MAF sensor inlet, large intake manifold or EGR leaks, or large leaks downstream of MAF sensor. Repair as necessary. After repairs, go to step 14). If no problems are found, go to next step.
5. Turn ignition off. Disconnect MAF sensor harness connector. Turn ignition on, with engine off. Check voltage between MAF sensor harness connector terminal "A" (signal circuit) and ground. If voltage reading is 5 volts, go to next step. If voltage reading is not 5 volts, go to step 9).
6. Connect test light between MAF sensor harness connector terminal "C" (ignition feed) and ground. If test light illuminates, go to step 8). If test light does not illuminate, go to next step.
7. Connect test light between MAF sensor harness connector terminal "C" and battery negative terminal. If test light illuminates, go to step 10). If test light does not illuminate, go to step 11).
8. Check for poor connection at MAF sensor. Repair as necessary. After repairs, go to step 14). If connections are okay, go to step 12).
9. Check circuit between MAF sensor PCM for an open, short to ground, short to MAF sensor ground circuit, or short to voltage. Repair as necessary. After repairs, go to step 14). If circuits are okay, go to step 13).
10. Locate and repair open in ground circuit to MAF sensor. After repairs, go to step 14).
11. Locate and repair open in ignition feed circuit to MAF sensor. After repairs, go to step 14).
12. Replace MAF sensor. After replacing MAF sensor, go to step 14).
13. Replace PCM. After replacing PCM, go to next step.
14. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC number that was set. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
15. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Check wiring harness for damage. If harness appears to be okay, observe scan tool while moving connectors and wiring harnesses related to the MAF sensor. A change in the display will indicate the location of fault.

Check for plugged intake air duct or dirty air filter. A wide-open throttle acceleration from a stop should cause the mass airflow displayed on scan tool to increase. If not, check for restrictions. If DTC P0102 cannot be duplicated, the information included in the Fail Records data can be useful in determining vehicle mileage since the DTC was last set and how often the DTC sets.

1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Start engine. With engine at idle, monitor MAF display on scan tool. If MAF reading is greater than 10496 Hz, go to step 4). If MAF reading is less than 10496 Hz, go to next step.
3. Turn engine off. Turn ignition on, with engine off. Review and record Fail Records data on scan tool. Operate vehicle within the Fail Records conditions as noted. Using scan tool, monitor SPECIFIC DTC information for DTC P0103. If scan tool indicates that DTC P0103 failed in this ignition cycle, go to next step. If DTC P0103 did not fail in this ignition cycle, see DIAGNOSTIC AIDS.
4. Turn ignition off. Disconnect MAF sensor harness connector. Start and idle engine. Using scan tool, monitor MAF display. If MAF value is 00 Hz, go to next step. If MAF value is not 00 Hz, go to step 7).
5. Check for poor connection at MAF harness connector terminals. Repair as necessary. After repairs, go to step 10). If terminals or connection is okay, go to next step.
6. Replace MAF sensor. After replacing MAF sensor, go to step 10).
7. Check MAF sensor harness for incorrect routing. Ensure there are no aftermarket add-ons near harness. Correct harness routing. After repairs, go to step 10). If no problems are found, go to next step.
8. Check MAF sensor signal circuit terminal connections at PCM. Repair as necessary. After repairs, go to step 10). If no problems are found, go to next step.
9. Replace PCM. After replacing PCM, go to next step.
10. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC number that was set. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
11. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Check wiring harness or terminals for damage. If harness or terminals appears to be okay, observe scan tool while moving connectors and wiring harnesses related to the MAF sensor. A change in the display will indicate the location of fault.

Note. Before clearing DTCs, record FREEZE FRAME and FAILURE RECORDS for reference during testing. Data will be erased when DTCs are cleared.

Note. If PCM is replaced, NEW PCM must be programmed using special equipment.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. Start engine. Monitor IAT display on scan tool. If IAT display is greater than or equal to 304°F (151°C), go to next step. If IAT display is less than 304°F (151°C), go to step 5).
3. Turn engine off. Disconnect IAT sensor connector. Turn ignition on. Monitor IAT display on scan tool. If IAT display is less than or equal to -30°F (-22°C), go to step 7). If IAT display is greater than specified, go to next step.
4. Turn ignition off. Using DVOM, check resistance between IAT sensor connector terminals. If resistance is infinite, go to step 8). If resistance is not infinite, go to step 6).
5. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
6. Repair short to ground in IAT signal circuit. After repairs, go to step 9).
7. Replace IAT sensor. After replacing sensor, go to step 9).
8. Replace PCM. After replacing PCM, go to next step.
9. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC that was set. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
10. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Check harness routing for a potential short to ground in signal circuit. Scan tool displays intake air temperature in degrees centigrade. See the TESTS W/O CODES article. A skewed sensor could result in poor driveability complaints.

Intake Air Temperature (IAT) Sensor Circuit Diagram. Scheme 15

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. Start engine. Monitor IAT display on scan tool. If IAT display is less than or equal to -22°F (-30°C), go to next step. If IAT display is greater than specified, go to step 5).
3. Turn engine off. Disconnect IAT sensor harness connector. Turn ignition on. Connect a jumper wire between IAT sensor connector terminals. Monitor IAT display on scan tool. If IAT display is greater than or equal to 304°F (151°C), go to step 6). If IAT display is less than 304°F (151°C), go to next step.
4. Connect a jumper wire between IAT signal circuit of IAT sensor connector and ground. Monitor IAT display on scan tool. If IAT display is greater than or equal to 304°F (151°C), go to step 7). If IAT display is less than 304°F (151°C), go to step 8).
5. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
6. Check for poor connections at IAT sensor and PCM. If a problem was found, go to step 9). If a problem is not found, go to step 10).
7. Check for open in IAT ground circuit between IAT sensor and PCM. If IAT ground circuit is open, go to step 9). If IAT ground circuit is not open, go to step 11).
8. Check for open in IAT signal circuit between IAT sensor and PCM. If IAT signal circuit is open, go to next step. If IAT signal circuit is not open, go to step 11).
9. Repair circuit as necessary. After repairs, go to step 12).
10. Replace IAT sensor. After replacing sensor, go to step 12).
11. Replace PCM. After replacing PCM, go to next step.
12. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC that was set. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
13. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Scan tool displays intake air temperature in degrees centigrade. See the TESTS W/O CODES article. A skewed sensor could result in poor driveability complaints.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. Start engine. Monitor ECT display on scan tool. If ECT display is greater than or equal to 304°F (151°C), go to next step. If ECT display is less than 304°F (151°C), go to step 5).
3. Turn engine off. Disconnect ECT sensor connector. Turn ignition on. Monitor ECT display on scan tool. If ECT display is less than or equal to -22°F (-30°C), go to step 7). If ECT display is greater than -22°F (-30°C), go to next step.
4. Turn ignition off. Using DVOM, check resistance between ECT sensor connector terminals. If resistance is infinite, go to step 8). If resistance is not infinite, go to step 6).
5. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
6. Repair short to ground in ECT signal circuit. After repairs, go to step 9).
7. Replace ECT sensor. After replacing sensor, go to step 9).
8. Replace PCM. After replacing PCM, go to next step.
9. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0117. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
10. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Check harness routing for a potential short to ground. After engine is started, coolant temperature should rise steadily to about 185°F (85°C). See the TESTS W/O CODES article. A skewed sensor could result in poor driveability complaints.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. Start engine. Monitor ECT display on scan tool. If ECT display is less than or equal to -22°F (-30°C), go to next step. If ECT display is greater than -22°F (-30°C), go to step 5).
3. Turn engine off. Disconnect ECT sensor harness connector. Turn ignition on. Connect a jumper wire between ECT sensor connector terminals. Monitor ECT display on scan tool. If ECT display is greater than or equal to 304°F (151°C), go to step 6). If ECT display is less than 304°F (151°C), go to next step.
4. Connect a jumper wire between ECT sensor harness connector terminal "B" (signal circuit) and ground. Monitor ECT display on scan tool. If ECT display is greater than or equal to 304°F (151°C), go to step 7). If ECT display is less than 304°F (151°C), go to step 8).
5. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
6. Check for poor connections at ECT sensor and PCM. If a problem was found, go to step 9). If a problem is not found, go to step 10).
7. Check for open in ECT ground circuit between ECT sensor and PCM. If ECT ground circuit is open, go to step 9). If ECT ground circuit is not open, go to step 11).
8. Check for open in ECT signal circuit between ECT sensor and PCM. If ECT signal circuit is open, go to next step. If ECT signal circuit is not open, go to step 11).
9. Repair circuit as necessary. After repairs, go to step 12).
10. Replace ECT sensor. After replacing sensor, go to step 12).
11. Replace PCM. After replacing PCM, go to next step.
12. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0118. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
13. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Check harness routing for a potential short to ground. After engine is started, coolant temperature should rise steadily to about 185°F (85°C). See the TESTS W/O CODES article. A skewed sensor could result in poor driveability complaints.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. Turn ignition on, with engine off. Using scan tool, with throttle closed, observe APP voltages. APP 1 voltage should be .45-.95 volt. APP 2 voltage should be 4.0-4.5 volts. APP 3 voltage should be 3.6-4.1 volts. If voltages are as specified, go to next step. If voltages are not as specified, go to step 4).
3. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
4. Turn ignition off. Disconnect APP sensor connector. Turn ignition on, with engine off. Using DVOM, probe 5-volt reference circuits (terminals "D", "E" and "G") of APP sensor connectors to ground. If voltage on all circuits is equal or greater than 4.75 volts, go to next step. If voltage on all circuits is not equal or greater than 4.75 volts, go to step 6).
5. Turn ignition on, with engine off. Using test light, probe ground circuits (terminals "A", "B" and "J") of APP sensor connectors to battery voltage. If test light illuminates on all circuits, go to step 9). If test light does not illuminate on all circuits, go to step 8).
6. Turn ignition off. Disconnect PCM harness connector. Check for open or short to ground in 5-volt reference circuits. Repair as necessary. If open or short to ground was present in 5-volt reference circuits, go to step 11). If open or short to ground was not present in 5-volt reference circuits, go to next step.
7. Check for poor connections at 5-volt reference terminals of PCM. Repair as necessary. If no repairs were required, go to step 11). If no terminals were replaced, go to step 10).
8. Turn ignition off. Disconnect PCM harness connector. Check for open in ground circuits. Repair as necessary. If open was present in ground circuits, go to step 11). If open was not present in ground circuits, go to step 10).
9. Replace APP module. After replacing module, go to step 11).
10. Replace PCM. After replacing PCM, go to next step.
11. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0121. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
12. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Scan tool reads APP 1 position in volts. With throttle closed and ignition on or at idle, voltage should be .45-.95 volt. Voltage should increase at a steady rate as throttle is moved toward Wide Open Throttle (WOT). Ninety percent pedal travel is acceptable for correct APP operation. Scan APP 1 sensor while depressing accelerator pedal with engine off and ignition on. Display should vary from about .74 volt with throttle closed to greater than 3.7 volts with throttle held at WOT.

Diagnostic procedures checks if all APP circuit voltages fall within normal ranges. PCM compares pre-scaled voltages (voltages scan tool can not read). Scan tool reads only output voltages.

Accelerator Pedal Position (APP) Module Diagram. Scheme 16

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. Turn ignition on, with engine off. Using scan tool, with throttle closed, observe APP 1 voltage. If APP 1 voltage is less than or equal to .25 volt, go to next step. If APP 1 voltage is greater than .25 volt, go to step 4).
3. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
4. Turn ignition off. Disconnect APP sensor connector. Connect a jumper wire between 5-volt reference circuit and signal circuit of APP 1 sensor connector. Using scan tool, observe APP 1 voltage. If APP 1 voltage is greater than 4.75 volts, go to step 10). If APP 1 voltage is less than 4.75 volts, go to next step.
5. Connect test light between signal circuit of APP 1 sensor connector and battery voltage. Using scan tool, observe APP 1 voltage. If APP 1 voltage is greater than 4.75 volts, go to next step. If APP 1 voltage is less than 4.75 volts, go to step 8).
6. Turn ignition off. Disconnect PCM harness connector. Check for open or short to ground in 5-volt reference circuit. Repair as necessary. If open or short to ground was present in 5-volt reference circuit, go to step 12). If open or short to ground was not present in 5-volt reference circuit, go to next step.
7. Check for poor connections at 5-volt reference terminals of PCM. Repair terminals as necessary. If any terminals were replaced, go to step 12). If no terminals were replaced, go to step 11).
8. Turn ignition off. Disconnect PCM harness connector. Check for open or short to ground in APP 1 signal circuit. Repair as necessary. If open or short to ground was present in APP 1 signal circuit, go to step 12). If open or short to ground was not present in APP 1 signal circuit, go to next step.
9. Check for poor connections at APP 1 signal terminal of PCM. Repair terminal as necessary. If terminal was replaced, go to step 12). If terminal was not replaced, go to step 11).
10. Replace APP module. After replacing module, go to step 12).
11. Replace PCM. After replacing PCM, go to next step.
12. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0122. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
13. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Scan tool reads APP 1 position in volts. With throttle closed and ignition on or at idle, voltage should be .45-.95 volt. Voltage should increase at a steady rate as throttle is moved toward Wide Open Throttle (WOT). Ninety percent pedal travel is acceptable for correct APP operation. Scan APP 1 sensor while depressing accelerator pedal with engine stopped and ignition on. Display should vary from about .74 volt with throttle closed to greater than 3.7 volts with throttle held at WOT. DTC will set if signal or 5-volt reference circuit are open.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. Turn ignition on, with engine off. Using scan tool, with throttle closed, observe APP 1 voltage. If APP 1 voltage is greater than 4.75 volts, go to step 4). If APP 1 voltage is less than 4.75 volts, go to next step.
3. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
4. Disconnect APP sensor connector. Using scan tool, observe APP 1 voltage. If APP 1 voltage is less than .25 volt, go to next step. If APP 1 voltage is greater than .25 volt, go to step 6).
5. Using test light, probe APP 1 ground circuit of APP 1 sensor connector to battery voltage. If test light illuminates, go to step 7). If test light does not illuminate, go to step 8).
6. Check for short to voltage in APP 1 signal circuit. Repair as necessary. If short to voltage was present in APP 1 signal circuit, go to step 11). If short to voltage was not present in APP 1 signal circuit, go to step 10).
7. Check for poor connections at APP sensor connector or a short to battery voltage in 5-volt reference circuit. Repair as necessary. After repairs, go to step 11). If no problems were found, go to step 10).
8. Check for open in APP 1 ground circuit. Repair as necessary. If open was present in APP 1 ground circuit, go to step 11). If open was not present in APP 1 ground circuit, go to step 10).
9. Replace APP module. After replacing module, go to step 11).
10. Replace PCM. After replacing PCM, go to next step.
11. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0123. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
12. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Scan tool reads APP 1 position in volts. With throttle closed and ignition on or at idle, voltage should be .45-.95 volt. Voltage should increase at a steady rate as throttle is moved toward Wide Open Throttle (WOT). Ninety percent pedal travel is acceptable for correct APP operation. Scan APP 1 sensor while depressing accelerator pedal with engine stopped and ignition on. Display should vary from about .74 volt with throttle closed to greater than 3.7 volts with throttle held at WOT. DTC will set if ground circuit is open or signal circuit is shorted to voltage.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Check if any engine coolant temperature DTC(s) are present. If other DTC(s) are present, diagnose using affected DTC test. If no other DTC(s) are present, go to next step.
3. Turn ignition on, with engine off. Disconnect ECT harness connector. Using scan tool, check ECT sensor value. If ECT sensor value is less than -31°F (-35°C), go to next step. If ECT sensor value is greater than -31°F (-35°C), diagnose using DTC P0117 test.
4. Using a jumper wire, jumper ECT sensor harness connector terminals. If scan tool indicates ECT is greater than 302°F (150°C), go to next step. If ECT value is less than 302°F (150°C), diagnose using DTC P0118 test.
5. Reconnect ECT sensor harness connector. Start and warm engine to normal operating temperature. Select ENGINE 1 DATA LIST on scan tool and observe ECT sensor display. If scan tool display reads that engine coolant temperature reached 140°F (60°C), recheck system on a cold start and refer to DIAGNOSTIC AIDS. If scan tool display does not indicate that engine coolant temperature has reached 140°F (60°C), go to next step.
6. Using DVOM, check ECT sensor resistance. See the SYSTEM/COMPONENT TESTS article. If resistance is not as specified, go to next step. If resistance is as specified, go to step 8).
7. Check thermostat operation, coolant level, coolant mixture ratio and cooling fan operation. Repair as necessary. After checking cooling system, go to step 9).
8. Replace ECT sensor. After replacing sensor, go to next step.
9. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC that was set. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
10. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Using Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If DTC cannot be duplicated, these information can be useful in determining how many times since the DTC set. The Fail Counter and Pass Counter can also be used to determine how many ignition cycles the diagnostic reported a pass and/or a fail. Operate vehicle with the same Freeze Frame conditions (RPM, load, vehicle speed, temperature, etc.) that were noted.

If other DTC(s) are set that share the same ground and/or 5-volt reference circuit, check for faulty connections or wiring. If engine has been allowed to sit overnight, ECT sensor and IAT sensor values should display within a few degrees of each other.

If engine coolant temperature exceeds 140°F (60°C), this indicates that the engine is capable of reaching proper temperature, but not necessarily in the correct amount of time. This test must be repeated on a cold engine, engine coolant and intake air temperature at less than 122°F (50°C) and within 5°F (3°C) of each other, and the time required to reach the temperature threshold must be measured.

The engine should reach the specified temperature within 8 minutes. If specified temperature is not reached within the specified time, check the cooling system.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. Start engine. Monitor fuel temperature display on scan tool. If fuel temperature display is greater than 215°F (102°C), go to next step. If fuel temperature display is less than 215°F (102°C), go to step 5).
3. Turn engine off. Disconnect optical/fuel temperature sensor connector. Turn ignition on. Monitor fuel temperature display on scan tool. If fuel temperature display is less than or equal to 63°F (17°C), go to step 7). If fuel temperature display is greater than 63°F (17°C), go to next step.
4. Turn ignition off. Using DVOM, check resistance between fuel temperature sensor connector terminals. If resistance is infinite, go to step 8). If resistance is not infinite, go to step 6).
5. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
6. Repair short to ground in fuel temperature signal circuit. Go to step 9).
7. Replace fuel injection pump. If fuel injection pump is replaced, new pump must be timed. See the «ADJUSTMENTS - 6.5L DIESEL»(ref-20564) article. After repairs, go to step 9).
8. Replace PCM. After replacing PCM, go to next step.
9. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0182. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
10. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Scan tool displays fuel temperature in degrees centigrade. After engine is started, fuel temperature should rise steadily.

Fuel Temperature Sensor Circuit Diagram. Scheme 17

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. Start engine. Monitor fuel temperature display on scan tool. If fuel temperature display is less to 63°F (17°C), go to next step. If display is greater than 63°F (17°C), go to step 5).
3. Turn engine off. Disconnect optical/fuel temperature sensor connector. Turn ignition on. Connect a jumper wire between fuel temperature sensor connector terminals. Monitor fuel temperature display on scan tool. If fuel temperature display is greater than 221°F (105°C), go to step 6). If fuel temperature display is less than 221°F (105°C), go to next step.
4. Connect a jumper wire between fuel temperature signal circuit of fuel temperature sensor connector and ground. Monitor fuel temperature display on scan tool. If fuel temperature display is greater than 221°F (105°C), go to step 7). If fuel temperature display is less than 221°F (105°C), go to step 8).
5. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
6. Check for poor connections at fuel temperature sensor and PCM. Repair as necessary. After repairs, go to step 9). If connections are okay, go to step 10).
7. Check for open in fuel temperature ground circuit between fuel temperature sensor and PCM. If fuel temperature ground circuit is open, go to step 9). If ground circuit is not open, go to step 11).
8. Check for open in fuel temperature signal circuit between fuel temperature sensor and PCM. If fuel temperature signal circuit is open, go to next step. If fuel temperature signal circuit is not open, go to step 11).
9. Repair circuit as necessary. After repairs, go to step 12).
10. Replace fuel injection pump. If fuel injection pump is replaced, new pump must be timed. See the «ADJUSTMENTS - 6.5L DIESEL»(ref-20564) article. After repairs, go to step 12).
11. Replace PCM. After replacing PCM, go to next step.
12. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0183. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
13. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Scan tool displays fuel temperature in degrees centigrade. After engine is started, fuel temperature should rise steadily. DTC will set if a faulty connection is present or signal circuit is open.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Ignition off. Disconnect Engine Shutoff (ESO) harness connector. Turn ignition on, with engine off. Using test light connected to ground, probe ESO harness connector terminal "B" (ignition feed). If test light is on, go to next step. If test light does not illuminate, go to step 5).
3. Turn ignition off. Using test light, jumper ESO harness connector terminals together. Turn ignition on, with engine off. If test light illuminates, go to next step. If test light does not illuminate, go to step 6).
4. Check the ESO and PCM harness connectors for poor connections. Repair or replace terminals as necessary. After repairs, go to step 9). If connectors and terminals are okay, go to step 7).
5. Check ESO ignition feed circuit for open or faulty fuse and repair as necessary. After repairs, go to step 9).
6. Check for open, poor PCM connection or circuit shorted to ground. Repair as necessary. After repairs, go to step 9). If circuits are okay, go to step 8).
7. Replace injection pump. After replacing injection pump, go to step 9).
8. Replace PCM. Program PCM using required equipment. After replacing PCM, go to next step.
9. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0215. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
10. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

DTC will set if control circuit or ignition feed circuit is open. A no start condition will also exist. Scan tool has capability to turn engine shutoff solenoid on and off. This can be a quick operational check of solenoid.

Engine Shutoff Solenoid Control Circuit Diagram. Scheme 18

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. Start and warm engine to normal operating temperature. Scan injection timing at idle and at 1500 RPM using scan tool. If scan tool displays a difference of 5 degrees between actual and desired injection time at idle and at 1500 RPM, go to next step. If scan tool does not display a difference of 5 degrees between actual and desired injection time at idle and at 1500 RPM, go to step 4).
3. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
4. Turn ignition off. Disconnect PCM harness connector. Using DVOM, check resistance between coil 1 low and coil 1 high circuits of PCM harness connector. If resistance is 10-60 ohms, go to next step. If resistance is not 10-60 ohms, go to step 10).
5. Using DVOM, check resistance between coil 2 low and coil 2 high circuits of PCM harness connector. If resistance is 10-60 ohms, go to next step. If resistance is not 10-60 ohms, go to step 9).
6. Reconnect PCM harness connector. Disconnect injection timing stepper motor harness connector. Start and idle engine. Using scan tool, command time set on. Using DVOM, check for a varying voltage between ground and each terminal of injection timing stepper motor connector. If voltage varies, go to next step. If voltage does not vary, go to step 11).
7. Disconnect crankshaft position sensor harness connector. Using DVOM, check resistance between crankshaft position sensor signal circuit and 5-volt reference circuit of crankshaft position sensor pigtail. If resistance is 950-1050 ohms, go to next step. If resistance is not 950-1050 ohms, go to step 12).
8. Reconnect sensor harness connector. Check if injection timing is set correctly. Check for a sheared camshaft driven key. Repair as necessary. After repairs, go to step 17). If a problem was not found, go to step 15).
9. Turn ignition off. Disconnect stepper motor harness connector. Check for open in coil 1 low and coil 1 high circuits. Repair as necessary. After repairs, go to step 17). If circuits are okay, go to next step.
10. Check for poor connections at injection timing stepper motor. Repair terminals as necessary. After repairs, go to step 17). If terminals are okay, go to step 15).
11. Check for short to ground in any injection timing stepper motor circuits or for poor connections at PCM. Repair as necessary. After repairs, go to step 17). If circuit or connection is okay, go to step 16).
12. Check for short to ground in crankshaft position sensor pigtail. Repair as necessary. After repairs, go to step 17). If circuits are okay, go to step 14).
13. Check for poor connection. Repair as necessary. After repairs, go to step 17). If connection and terminals are okay, go to step 16).
14. Replace crankshaft position sensor. After replacing sensor, go to step 17).
15. Replace fuel injection pump. If fuel injection pump is replaced, new pump must be timed. See the «ADJUSTMENTS - 6.5L DIESEL»(ref-20564) article. After replacing pump, go to step 17).
16. Replace PCM. After replacing PCM, go to next step.
17. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0216. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
18. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

An intermittent may be caused by poor connections, rubbed through wire insulation or broken wire inside insulation. A hard start and possible poor performance may exist. Actual injection time will freeze at point of fault. DTC could set if injection timing is not correctly set. See the ADJUSTMENTS - 6.5L DIESEL article.

Injection Timing Control System Diagram. Scheme 19

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Replace fuel injection pump. If fuel injection pump is replaced, new pump must be timed. See the «ADJUSTMENTS - 6.5L DIESEL»(ref-20564) article. After replacing fuel injection pump, go to next step.
3. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0219. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
4. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

DTC will not set if an external fuel source is causing an overspeed condition. DTC P1216 will also set if DTC P0219 is set.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Turn ignition off. Disconnect APP sensor connector. Turn ignition on, with engine off. Using DVOM, check voltage between ground and 5-volt reference circuits (terminals "D", "E" and "G") of APP sensor connectors. If voltage on all circuits is less than 4.8 volts, go to step 4). If voltage on all circuits is not less than 4.8 volts, go to next step.
3. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
4. Turn ignition off. Disconnect PCM harness connector. Check for short to ground in 5-volt reference circuits. Repair as necessary. If short to ground was present in 5-volt reference circuits, go to step 6). If short to ground was not present in 5-volt reference circuits, go to next step.
5. Replace PCM. After replacing PCM, go to next step.
6. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0220. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
7. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Most likely cause of DTC is loose connectors or terminals. All 5-volt reference circuits must be checked for proper reference voltage.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. Turn ignition on, with engine off. Using scan tool, with throttle closed, observe APP voltages. APP 1 voltage should be .45-.95 volt. APP 2 voltage should be 4.0-4.5 volts. APP 3 voltage should be 3.6-4.0 volts. If voltages are as specified, go to next step. If voltages are not as specified, go to step 4).
3. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
4. Turn ignition off. Disconnect APP sensor harness connector. Turn ignition on, with engine off. Using DVOM, probe 5-volt reference circuits (terminals "D", "E" and "G") of APP sensor connectors to ground. If voltage on all circuits is 4.75 volts, go to next step. If voltage on all circuits is not 4.75 volts, go to step 6).
5. Turn ignition on, with engine off. Using test light, probe ground circuits (terminals "A", "B" and "J") of APP sensor connectors to battery voltage. If test light illuminates on all circuits, go to step 9). If test light does not illuminate on all circuits, go to step 8).
6. Turn ignition off. Disconnect PCM harness connector. Check for open or short to ground in 5-volt reference circuits. Repair as necessary. If circuit is open or shorted to ground, repair as necessary and go to step 11). If circuit is okay, go to next step.
7. Check for poor connections at 5-volt reference terminals of PCM. Repair terminals as necessary. After repairs, go to step 11). If connections are okay, go to step 10).
8. Turn ignition off. Disconnect PCM harness connector. Check for open in ground circuits. Repair as necessary. After repairs, go to step 11). If circuits are okay, go to step 10).
9. Replace APP module. After replacing module, go to step 11).
10. Replace PCM. After replacing PCM, go to next step.
11. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0221. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
12. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Scan tool reads APP 2 position in volts. With throttle closed and ignition on or at idle, voltage should be 4.5 volts. Voltage should decrease at a steady rate as throttle is moved toward Wide Open Throttle (WOT). Ninety percent pedal travel is acceptable for correct APP operation. See the TESTS W/O CODES article. Scan APP 2 sensor while depressing accelerator pedal with engine stopped and ignition on. Display should vary from about 4.5 volts with throttle closed to about 1.5 volts with throttle held at WOT.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. Turn ignition on, with engine off. Using scan tool, with throttle closed, observe APP 2 voltage. If APP 2 voltage is less than or equal to .25 volt, go to step 4). If APP 2 voltage is greater than .25 volt, go to next step.
3. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
4. Turn ignition off. Disconnect APP sensor harness connector. Using DVOM, check voltage on APP 2 sensor connector 5-volt reference circuit terminal. If voltage is greater than 5 volts, go to step 5). If voltage is less than 5 volts, go to step 6).
5. Using DVOM, check voltage on APP 2 sensor connector signal circuit terminal. If voltage is greater than 5 volts, go to step 10). If voltage is 5 volts or less, go to step 8).
6. Turn ignition off. Disconnect PCM harness connector. Check for open or short to ground in 5-volt reference circuits. Repair as necessary. After repairs, go to step 12). If circuits are okay, go to next step.
7. Check for poor connections at 5-volt reference terminals of PCM. Repair terminals as necessary. After repairs, go to step 12). If connections are okay, go to step 11).
8. Turn ignition off. Disconnect PCM harness connector. Check for open or short to ground in APP 2 signal circuit. Repair as necessary. After repairs, go to step 12). If circuits are okay, go to next step.
9. Check for poor connections at APP sensor terminal and at PCM. Repair terminal as necessary. After repairs, go to step 12). If terminal connections are okay, go to step 11).
10. Replace APP module. After replacing module, go to step 12).
11. Replace PCM. After replacing PCM, Go to next step.
12. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0222. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
13. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Scan tool reads APP 2 position in volts. With throttle closed and ignition on or at idle, voltage should be 4.5 volts. Voltage should decrease at a steady rate as throttle is moved toward Wide Open Throttle (WOT). See the TESTS W/O CODES article. Scan APP 2 sensor while depressing accelerator pedal with engine stopped and ignition on. Display should vary from about 4.5 volts with throttle closed to about 1.5 volts with throttle held at WOT.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. Turn ignition on, with engine off. Using scan tool, with throttle closed, observe APP 2 voltage. If APP 2 voltage is greater than or equal to 4.75 volts, go to step 4). If APP 2 voltage is less than 4.75 volts, go to next step.
3. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
4. Using a test light, probe APP 2 ground circuit of APP 2 sensor connector to battery voltage. If test light illuminates, go to next step. If test light does not illuminate, go to step 7).
5. Disconnect APP sensor harness connector. Using a fused jumper wire, jumper APP 2 signal circuit to APP 2 ground circuit. Using scan tool, observe APP 2 voltage. If APP 2 voltage is less than .25 volt, go to step 8). If APP 2 voltage is greater than .25 volt, go to next step.
6. Check for an open in APP 2 signal circuit. Repair as necessary. After repairs, go to step 11). If circuit is okay, go to step 10).
7. Check for open in APP 2 ground circuit. Repair as necessary. After repairs, go to step 11). If circuit is okay, go to step 10).
8. Check for poor connections at APP sensor connector. Repair terminals as necessary. After repairs, go to step 11). If terminals are okay, go to next step.
9. Replace APP module. After replacing module, go to step 11).
10. Replace PCM. After replacing PCM, go to next step.
11. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0223. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
12. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Scan tool reads APP 2 position in volts. With throttle closed and ignition on or at idle, voltage should be 4.5 volts. Voltage should decrease at a steady rate as throttle is moved toward Wide Open Throttle (WOT). Ninety percent pedal travel is acceptable for correct APP operation. See the TESTS W/O CODES article. Scan APP 2 sensor while depressing accelerator pedal with engine stopped and ignition on. Display should vary from about 4.5 volts with throttle closed to about 1.5 volts with throttle held at WOT. If signal circuit is open, P1125 could also be set when P0223 sets.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Turn ignition off. Disconnect APP sensor harness connector. Turn ignition on, with engine off. Using DVOM, check voltage between ground and 5-volt reference circuits (terminals "D", "E" and "G") of APP sensor harness connectors. If voltage on all circuits is 4.8 volts, go to step 4). If voltage on all circuits is not 4.8 volts, go to next step.
3. If any other APP DTCs are set, diagnose affected DTC. If other DTCs are not present, go to next step.
4. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
5. Turn ignition off. Disconnect PCM harness connector. Check for short to ground in 5-volt reference circuits. Repair as necessary. After repairs, go to step 7). If circuits are okay, go to next step.
6. Replace PCM. After replacing PCM, go to next step.
7. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0225. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
8. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

All 5-volt reference circuits must be checked for proper reference voltage.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. Turn ignition on, with engine off. Using scan tool, with throttle closed, observe APP voltages. APP 1 voltage should be .45-.95 volt. APP 2 voltage should be 4.0-4.5 volts. APP 3 voltage should be 3.6-4.0 volts. If voltages are as specified, go to next step. If voltages are not as specified, go to step 4).
3. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
4. Turn ignition off. Disconnect APP sensor harness connector. Turn ignition on, with engine off. Using DVOM, probe 5-volt reference circuits (terminals "D", "E" and "G") of APP sensor connectors to ground. If voltage on all circuits are 4.75 volts, go to next step. If voltage on all circuits are not 4.75 volts, go to step 6).
5. Turn ignition on, with engine off. Using a test light, probe ground circuits (terminals "A", "B" and "J") of APP sensor connectors to battery voltage. If test light illuminates on all circuits, go to step 9). If test light does not illuminate on all circuits, go to step 8).
6. Turn ignition off. Disconnect PCM harness connector. Check for open or short to ground in 5-volt reference circuits. Repair as necessary. After repairs, go to step 11). If circuits are okay, go to next step.
7. Check for poor connections at 5-volt reference terminals of PCM. Repair terminals as necessary. After repairs, go to step 11). If connections are okay, go to step 10).
8. Turn ignition off. Disconnect PCM harness connector. Check for open in ground circuits. Repair as necessary. After repairs, go to step 11). If circuits are okay, go to step 10).
9. Replace APP module. After replacing module, go to step 11).
10. Replace PCM. After replacing PCM, go to next step.
11. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0226. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
12. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Scan tool reads APP 3 position in volts. With throttle closed and ignition on or at idle, voltage should be 4 volts. Voltage should decrease at a steady rate as throttle is moved toward Wide Open Throttle (WOT). Ninety percent pedal travel is acceptable for correct APP operation. Scan APP 3 sensor while depressing accelerator pedal with engine stopped and ignition on. Display should vary from about 4 volts with throttle closed to about 2 volts with throttle held at WOT.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. Turn ignition on, with engine off. Using scan tool, with throttle closed, observe APP 3 voltage. If APP 3 voltage is less than or equal to .25 volt, go to step 4). If APP 3 voltage is greater than .25 volt, go to next step.
3. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
4. Turn ignition off. Disconnect APP sensor harness connector. Connect a jumper wire between 5-volt reference circuit and signal circuit of APP 3 sensor connector. Using scan tool, observe APP 3 voltage. If APP 3 voltage is about 5 volts, go to next step. If voltage is not about 5 volts, go to step 6).
5. Using DVOM, probe APP 3 sensor harness signal circuit terminal. If voltage is about 5 volts, go to step 10). If voltage is not about 5 volts, go to step 8).
6. Turn ignition off. Disconnect PCM harness connector. Check for open or short to ground in 5-volt reference circuits. Repair as necessary. After repairs, go to step 13). If circuits are okay, go to next step.
7. Check for poor connections at 5-volt reference terminals of PCM. Repair terminals as necessary. After repairs, go to step 13). If connections are okay, go to step 12).
8. Turn ignition off. Disconnect PCM harness connector. Check for open or short to ground in APP 3 signal circuit. Repair as necessary. After repairs, go to step 13). If circuits are okay, go to next step.
9. Check for poor connections at APP 3 signal terminal at PCM. Repair terminal as necessary. After repairs, go to step 13). If terminal is okay, go to step 12).
10. Check for poor electrical connection at APP sensor. Repair as necessary. After repairs, go to step 13). If connection is okay, go to next step.
11. Replace APP module. After replacing module, go to step 13).
12. Replace PCM. After replacing PCM, go to next step.
13. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0227. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
14. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Scan tool reads APP 3 position in volts. With throttle closed and ignition on or at idle, voltage should be 4 volts. Voltage should decrease at a steady rate as throttle is moved toward Wide Open Throttle (WOT). Ninety percent pedal travel is acceptable for correct APP operation. See the TESTS W/O CODES article. Scan APP 3 sensor while depressing accelerator pedal with engine stopped and ignition on. Display should vary from about 4 volts with throttle closed to about 2 volts with throttle held at WOT.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. Turn ignition on, with engine off. Using scan tool, with throttle closed, observe APP 3 voltage. If APP 3 voltage is greater than 4.75 volts, go to step 4). If APP 3 voltage is less than 4.75 volts, go to next step.
3. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
4. Disconnect APP harness connector. Using a test light, probe APP 3 ground circuit of APP 3 sensor connector to battery voltage. If test light illuminates, go to next step. If test light does not illuminate, go to step 7).
5. Using a fused jumper, connect APP 3 harness signal circuit and ground circuit terminals together. Using scan tool, observe APP 3 voltage. If APP 3 voltage is less than .25 volt, go to step 8). If APP 3 voltage is greater than .25 volt, go to next step.
6. Check for open in APP 3 sensor signal circuit. Repair as necessary. After repairs, go to step 11). If circuit is okay, go to step 10).
7. Check for open sensor ground circuit. Repair as necessary. After repairs, go to step 11). If circuit is okay, go to step 10).
8. Check for poor connections at APP sensor harness connector. Repair terminals as necessary. After repairs, go to step 11). If connections are okay, go to next step.
9. Replace APP module. After replacing module, go to step 11).
10. Replace PCM. After replacing PCM, go to next step.
11. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0228. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
12. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Scan tool reads APP 3 position in volts. With throttle closed and ignition on or at idle, voltage should be 4 volts. Voltage should decrease at a steady rate as throttle is moved toward Wide Open Throttle (WOT). Ninety percent pedal travel is acceptable for correct APP operation. Scan APP 3 sensor while depressing accelerator pedal with engine stopped and ignition on. Display should vary from about 4 volts with throttle closed to about 2 volts with throttle held at WOT.

Circuit Description

PCM monitors status of lift pump. Signal is also used store a DTC if fuel pump relay is defective or fuel pump voltage is lost while engine is running. About 12 volts should be present on fuel pump signal circuit during glow plug cycle.

DTC will set when the following conditions are present

1. Fuel lift pump is commanded on.
2. Difference between ignition voltage and fuel pump voltage is greater than 4 volts.
3. Conditions are met for 2 seconds.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. Turn ignition on, with engine off. Using scan tool, command fuel pump on. If fuel pump operates, see DIAGNOSTIC AIDS. If fuel pump does not operate, go to next step.
3. Turn ignition off. Using a DVOM connected to ground, backprobe fuel lift pump signal circuit at PCM harness connector. Using a fused jumper wire connected to battery voltage, jumper fuel pump test terminal. If DVOM reads battery voltage, go to step 8). If DVOM does not read battery voltage, go to next step.
4. Remove fuel pump relay. Using a fused jumper wire connected to battery voltage, probe fuel pump relay terminal A3 from underneath fuse/relay block. If DVOM reads battery voltage, go to next step. If DVOM does not read battery voltage, go to step 6).
5. Check for poor connection at fuse/relay block to fuel pump relay. Repair as necessary. After repairs, go to step 17).
6. Check for open or short to ground in fuel pump signal circuit. Repair as necessary. After repairs, go to step 18. If circuit is okay, go to next step.
7. Check for poor connection at PCM and fuse/relay block. Repair as necessary. After repairs, go to step 18). If connections are okay, go to step 15).
8. Remove fuel pump relay. Turn ignition on. Using a test light connected to ground, probe fuel pump relay harness connector terminal B1. If test light illuminates, go to step 10). If test light does not illuminate, go to next step.
9. Repair open in battery feed circuit to fuel pump relay. After repairs, go to step 18).
10. Connect test light between fuel pump harness connector terminals A1 and B1. If test light illuminates, go to step 12). If test light does not illuminate, go to next step.
11. Repair open in fuel pump relay ground circuit. After repairs, go to step 18).
12. Turn ignition off. Connect test light between fuel pump relay harness connector terminal B3 and ground. Turn ignition on. If test light illuminates during the glow plug cycle then turns off, go to step 16). If test light does not illuminate during the glow plug cycle, go to next step.
13. Check for open in fuel pump relay harness connector terminal B3 and PCM. Repair as necessary. After repairs, go to next step. If circuit is okay, go to step 15).
14. Repair open in fuel pump control circuit. After repairs, go to step 18).
15. Replace PCM. After replacing PCM, go to step 18).
16. Check for poor connection at control circuit of fuel pump relay. Repair as necessary. After repairs, go to step 18). If circuit is okay, go to next step.
17. Replace fuel pump relay. After replacing relay, go to next step.
18. After repairs, use CLEAR INFO function on scan tool and road test vehicle. Check for current or history DTC(s). Review test status information. If scan tool indicates that the test failed or DTC(s) are present, diagnose using affected DTC test. After repairs, go to next step.
19. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

This DTC will not check for fuel pump operation.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Check if DTC P1656 is also set. If DTC P1656 is present, diagnose this DTC first. See DTC P1656 test. If DTC P1656 is not present, go to next step.
3. Disconnect vacuum hose from turbocharger wastegate actuator. Install vacuum gauge to vacuum hose. Start engine. With engine at idle, vacuum reading should be 15 in. Hg. If vacuum reading is equal or greater than 15 in. Hg, go to next step. If vacuum reading is less than 15 in. Hg, go to step 6).
4. Disconnect wastegate solenoid harness connector. With engine running, check vacuum gauge reading. If vacuum reading is greater than 1 in. Hg, go to step 10). If vacuum reading is less than 1 in. Hg, go to next step.
5. Turn engine off. Connect a hand-held vacuum pump to wastegate actuator. Apply 5 in. Hg of vacuum to actuator. If actuator holds vacuum, go to step 7). If actuator does not hold vacuum, go to step 12).
6. Check all vacuum lines from vacuum pump to wastegate actuator for leaks, deformities or pinches. Repair as necessary. After repairs, go to step 13). If vacuum hoses are okay, go to step 9).
7. Ensure engine is off. Disconnect vacuum lines to wastegate actuator. Using a pair of pliers, grip wastegate actuator rod. Move actuator rod back and forth. If actuator rod moves freely, go to next step. If actuator rod does not move or does not move freely, go to step 12).
8. DTC is intermittent. If no additional DTC(s) are present, see DIAGNOSTIC AIDS. If additional DTC(s) are present, diagnose affected DTC(s).
9. Check vacuum pump for proper output. Repair as necessary. After repairs, go to step 13).
10. Check for plugged wastegate solenoid filter. Repair or replace as necessary. After repairs, go to step 13). If filter is okay, go to next step.
11. Replace wastegate solenoid. After replacing solenoid, go to step 13).
12. Replace turbocharger actuator. After replacing actuator, go to next step.
13. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0236. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
14. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

A vacuum leak or pinched vacuum line could cause DTC P0236 to set. Check all vacuum lines and components connected to hoses for leaks or sharp bends. Check vacuum source. A possible EGR DTC will set if problem is present with vacuum source. Check for proper vacuum line routing.

The turbocharger wastegate actuator uses a pulse width modulated vacuum solenoid that causes vacuum to fluctuate under normal conditions. A steady vacuum reading indicates a restricted or plugged solenoid vent filter or solenoid vent orifice.

Turbocharger Boost System Diagram. Scheme 20

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. Operate engine at idle. Observe boost pressure on scan tool display. If boost pressure is equal to or less than 40 kPa, go to next step. If boost pressure is greater than 40 kPa, go to step 5).
3. Turn ignition off. Disconnect boost sensor harness connector. Connect a jumper wire between 5-volt reference and boost signal circuits of boost sensor connector. Turn ignition on. If scan tool displays a boost pressure greater than 202 kPa, go to step 6). If scan tool does not display a boost pressure greater than 202 kPa, go to next step.
4. Turn ignition off. Ensure boost sensor connector is still disconnected. Remove jumper wire. Connect test light between boost signal circuit of boost sensor connector and battery voltage. Turn ignition on. If scan tool displays a boost pressure of equals to or greater than 202 kPa, go to step 8). If scan tool does not display a boost pressure of equals to or greater than 202 kPa, go to step 7).
5. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to diagnose affected DTC(s).
6. Check for poor connections at boost sensor. If a problem was found, go to step 13). If a problem was not found, go to step 10).
7. Check for open or short to ground in boost signal circuit. If a problem was found, go to step 13). If a problem was not found, go to step 11).
8. Check for open in boost sensor 5-volt reference circuit. If a problem was found, go to step 13). If a problem was not found, go to next step.
9. Check for short to ground in boost sensor 5-volt reference circuit. If a problem was found, go to step 13). If a problem was not found, go to step 12).
10. Replace boost sensor. After replacing sensor, go to step 13).
11. Check for poor terminal connections at PCM. Repair as necessary. After repairs, go to step 13). If connections are okay, go to next step.
12. Replace PCM. After replacing PCM, go to next step.
13. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0237. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
14. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Very little boost can be attained by revving engine in Neutral. Boost solenoid will show zero duty cycle if boost sensor signal circuit is open or shorted to ground. DVOM can be used to measure (actual) signal voltage at PCM connector. An intermittent can be caused by poor connections, rubbed through wire insulation or broken wire inside the insulation.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. Operate engine at idle. Using scan tool, monitor boost pressure. If scan tool displays a boost pressure greater than or equal to 202 kPa, go to next step. If scan tool does not display a boost pressure of greater than or equal to 202 kPa, go to step 4).
3. Turn ignition off. Disconnect boost sensor harness connector. Using a fused jumper wire, probe boost signal circuit of boost sensor connector to ground. Turn ignition on. If scan tool displays a boost pressure less than or equal to 9 kPa, go to step 5). If scan tool does not display a boost pressure less than or equal to 9 kPa, go to step 9).
4. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
5. Turn ignition on, with engine off. Using DVOM connected to ground, probe 5-volt reference circuit terminal at boost sensor connector. If voltage is greater than 5.2 volts, go to step 10). If not, go to next step.
6. Leave boost sensor connector disconnected. Connect test light between boost ground circuit of boost sensor connector and battery voltage. If test light illuminates, go to next step. If test light does not illuminate, go to step 11).
7. Check boost sensor for restriction. If a problem was found, go to step 12). If a problem was not found, go to next step.
8. Replace boost sensor. After replacing sensor, go to step 14).
9. Check for short to voltage in boost signal circuit. Repair as necessary. After repairs, go to step 12). If circuit is okay, go to step 13).
10. Check for short to voltage in 5-volt reference circuit. Repair as necessary. After repairs, go to step 12). If circuit is okay, go to step 13).
11. Repair boost ground circuit as necessary. After repairs, go to step 14).
12. Replace PCM. After replacing PCM, go to next step.
13. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0238. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
14. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

With ignition on and engine off, boost pressure is equal to atmospheric pressure. To check accuracy of suspect sensor, compare reading with a known good vehicle with same sensor. Readings should be within .4 volt of each other. Very little boost can be attained by revving engine in Neutral. DVOM can be used to measure (actual) signal voltage at PCM connector.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. Start and operate engine at idle. Using scan tool, with throttle closed, observe CAM REF MISSED display. If scan tool displays at least "8", go to step 4). If scan tool does not display at least "8", go to next step.
3. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
4. Turn ignition off. Disconnect optical/fuel temperature sensor harness connector. Turn ignition on, with engine off. Using DVOM, check voltage between 5-volt reference circuit of optical sensor connector and ground. If voltage reading is 5 volts, go to next step. If voltage reading is not 5 volts, go to step 7).
5. Using a test light connected to battery voltage, probe ground circuit of optical sensor connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 8).
6. Reconnect optical/fuel temperature sensor connector. Start and idle engine. Using scan tool, command engine speed to 900 RPM. Using DVOM on Hz scale, backprobe cam signal circuit at PCM. If DVOM reading is 57-63 Hz, go to step 12). If DVOM reading is not 57-63 Hz, go to step 11).
7. Remove electrical harness filter from vehicle. Using DVOM, check resistance of filter harness. If resistance is greater than 2 ohms, go to step 15). If resistance is less than 2 ohms, go to next step.
8. Turn ignition off. Leave electrical filter removed from vehicle. Disconnect PCM harness connector. Check 5-volt reference circuit for open, short to ground, or short to sensor ground circuit. Repair as necessary. After repairs, go to step 16). If circuit is okay, go to step 10).
9. Check for open or poor connections at sensor ground terminals of PCM. Repair as necessary. After repairs, go to step 16). If connections are okay, go to step 14).
10. Check for poor connections at 5-volt reference terminals of PCM. Repair terminals as necessary. After repairs, go to step 16). If terminals are okay, go to step 14).
11. Turn ignition off. Check for open or short to ground in cam signal circuit. Repair as necessary. After repairs, go to step 16). If circuit is okay, go to step 13).
12. Check for poor connections at PCM. Repair terminals as necessary. After repairs, go to step 16). If terminals are okay, go to step 14).
13. Replace injection pump. If fuel injection pump is replaced, new pump must be timed. See the «ADJUSTMENTS - 6.5L DIESEL»(ref-20564) article. After replacing injection pump, go to step 16).
14. Replace PCM. After replacing PCM, go to step 16).
15. Replace electrical filter. After replacing filter, go to next step.
16. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0251. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
17. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Fast idle and poor performance will exist when PCM is in back-up fuel. If DTC P0370 is also set, possible problem exists with signal circuit. If vehicle runs out of fuel, DTCs P0251 and P0370 will set.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. Start and idle engine. Operate engine at normal operating temperature. Ensure all DTCs are cleared. Using scan tool, cut out (injector balance) suspected cylinder. If RPM drops in suspected cylinder, go to next step. If RPM does not drop in suspected cylinder, go to step 4).
3. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
4. Check for basic engine mechanical or fuel delivery problem in suspected cylinder. Repair as necessary. After repairs, go to step 6). If repairs were not necessary, go to next step.
5. Replace fuel injection pump. After replacing injection pump, go to next step.
6. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0263. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
7. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Injector balance test on scan tool should be used to confirm faulty cylinder. Scan tool will cut out specific cylinder requested. If is possible if a cylinder balance fault has been detected and engine has been running for a long time, PCM may try to increase or decrease fuel in other cylinders to compensate for rough idle which will cause multiple cylinder balance DTCs to set.

Scan tool snapshot mode can be used to properly identify suspected cylinder. Most likely cause of cylinder balance DTCs are faulty nozzles or engine mechanical (low compression) problems.

Fuel Line Routing Schematic. Scheme 21

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. Start and idle engine. Operate engine at normal operating temperature. Ensure all DTCs are cleared. Using scan tool, cut out (injector balance) suspected cylinder. If RPM drops in suspected cylinder, go to next step. If RPM does not drop in suspected cylinder, go to step 4).
3. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
4. Check for basic engine mechanical or fuel delivery problem in suspected cylinder. Repair as necessary. After repairs, go to step 6). If repairs were not necessary, go to next step.
5. Replace fuel injection pump. After replacing injection pump, go to next step.
6. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0263. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
7. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Injector balance test on scan tool should be used to confirm faulty cylinder. Scan tool will cut out specific cylinder requested. If is possible if a cylinder balance fault has been detected and engine has been running for a long time, PCM may try to increase or decrease fuel in other cylinders to compensate for rough idle which will cause multiple cylinder balance DTCs to set.

Scan tool snapshot mode can be used to properly identify suspected cylinder. Most likely cause of cylinder balance DTCs are faulty nozzles or engine mechanical (low compression) problems.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. Start and idle engine. Operate engine at normal operating temperature. Ensure all DTCs are cleared. Using scan tool, cut out (injector balance) suspected cylinder. If RPM drops in suspected cylinder, go to next step. If RPM does not drop in suspected cylinder, go to step 4).
3. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
4. Check for basic engine mechanical or fuel delivery problem in suspected cylinder. Repair as necessary. After repairs, go to step 6). If repairs were not necessary, go to next step.
5. Replace fuel injection pump. After replacing injection pump, go to next step.
6. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0263. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
7. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Injector balance test on scan tool should be used to confirm faulty cylinder. Scan tool will cut out specific cylinder requested. If is possible if a cylinder balance fault has been detected and engine has been running for a long time, PCM may try to increase or decrease fuel in other cylinders to compensate for rough idle which will cause multiple cylinder balance DTCs to set.

Scan tool snapshot mode can be used to properly identify suspected cylinder. Most likely cause of cylinder balance DTCs are faulty nozzles or engine mechanical (low compression) problems.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. Start and idle engine. Operate engine at normal operating temperature. Ensure all DTCs are cleared. Using scan tool, cut out (injector balance) suspected cylinder. If RPM drops in suspected cylinder, go to next step. If RPM does not drop in suspected cylinder, go to step 4).
3. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
4. Check for basic engine mechanical or fuel delivery problem in suspected cylinder. Repair as necessary. After repairs, go to step 6). If repairs were not necessary, go to next step.
5. Replace fuel injection pump. After replacing injection pump, go to next step.
6. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0263. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
7. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Injector balance test on scan tool should be used to confirm faulty cylinder. Scan tool will cut out specific cylinder requested. If is possible if a cylinder balance fault has been detected and engine has been running for a long time, PCM may try to increase or decrease fuel in other cylinders to compensate for rough idle which will cause multiple cylinder balance DTCs to set.

Scan tool snapshot mode can be used to properly identify suspected cylinder. Most likely cause of cylinder balance DTCs are faulty nozzles or engine mechanical (low compression) problems.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. Start and idle engine. Operate engine at normal operating temperature. Ensure all DTCs are cleared. Using scan tool, cut out (injector balance) suspected cylinder. If RPM drops in suspected cylinder, go to next step. If RPM does not drop in suspected cylinder, go to step 4).
3. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
4. Check for basic engine mechanical or fuel delivery problem in suspected cylinder. Repair as necessary. After repairs, go to step 6). If repairs were not necessary, go to next step.
5. Replace fuel injection pump. After replacing injection pump, go to next step.
6. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0263. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
7. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Injector balance test on scan tool should be used to confirm faulty cylinder. Scan tool will cut out specific cylinder requested. If is possible if a cylinder balance fault has been detected and engine has been running for a long time, PCM may try to increase or decrease fuel in other cylinders to compensate for rough idle which will cause multiple cylinder balance DTCs to set.

Scan tool snapshot mode can be used to properly identify suspected cylinder. Most likely cause of cylinder balance DTCs are faulty nozzles or engine mechanical (low compression) problems.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. Start and idle engine. Operate engine at normal operating temperature. Ensure all DTCs are cleared. Using scan tool, cut out (injector balance) suspected cylinder. If RPM drops in suspected cylinder, go to next step. If RPM does not drop in suspected cylinder, go to step 4).
3. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
4. Check for basic engine mechanical or fuel delivery problem in suspected cylinder. Repair as necessary. After repairs, go to step 6). If repairs were not necessary, go to next step.
5. Replace fuel injection pump. After replacing injection pump, go to next step.
6. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0263. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
7. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Injector balance test on scan tool should be used to confirm faulty cylinder. Scan tool will cut out specific cylinder requested. If is possible if a cylinder balance fault has been detected and engine has been running for a long time, PCM may try to increase or decrease fuel in other cylinders to compensate for rough idle which will cause multiple cylinder balance DTCs to set.

Scan tool snapshot mode can be used to properly identify suspected cylinder. Most likely cause of cylinder balance DTCs are faulty nozzles or engine mechanical (low compression) problems.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. Start and idle engine. Operate engine at normal operating temperature. Ensure all DTCs are cleared. Using scan tool, cut out (injector balance) suspected cylinder. If RPM drops in suspected cylinder, go to next step. If RPM does not drop in suspected cylinder, go to step 4).
3. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
4. Check for basic engine mechanical or fuel delivery problem in suspected cylinder. Repair as necessary. After repairs, go to step 6). If repairs were not necessary, go to next step.
5. Replace fuel injection pump. After replacing injection pump, go to next step.
6. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0263. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
7. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Injector balance test on scan tool should be used to confirm faulty cylinder. Scan tool will cut out specific cylinder requested. If is possible if a cylinder balance fault has been detected and engine has been running for a long time, PCM may try to increase or decrease fuel in other cylinders to compensate for rough idle which will cause multiple cylinder balance DTCs to set.

Scan tool snapshot mode can be used to properly identify suspected cylinder. Most likely cause of cylinder balance DTCs are faulty nozzles or engine mechanical (low compression) problems.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. Start and idle engine. Operate engine at normal operating temperature. Ensure all DTCs are cleared. Using scan tool, cut out (injector balance) suspected cylinder. If RPM drops in suspected cylinder, go to next step. If RPM does not drop in suspected cylinder, go to step 4).
3. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
4. Check for basic engine mechanical or fuel delivery problem in suspected cylinder. Repair as necessary. After repairs, go to step 6). If repairs were not necessary, go to next step.
5. Replace fuel injection pump. After replacing injection pump, go to next step.
6. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0263. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
7. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Injector balance test on scan tool should be used to confirm faulty cylinder. Scan tool will cut out specific cylinder requested. If is possible if a cylinder balance fault has been detected and engine has been running for a long time, PCM may try to increase or decrease fuel in other cylinders to compensate for rough idle which will cause multiple cylinder balance DTCs to set.

Scan tool snapshot mode can be used to properly identify suspected cylinder. Most likely cause of cylinder balance DTCs are faulty nozzles or engine mechanical (low compression) problems.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. Start and idle engine. Using scan tool, with throttle closed, observe CRANK REF MISSED display. If scan tool displays "8", go to step 4). If scan tool does not display "8", go to next step.
3. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
4. Turn ignition off. Disconnect CKP sensor connector. Turn ignition on, with engine off. Using DVOM, check voltage between 5-volt reference circuit of CKP sensor connector and ground. If voltage is 5 volts, go to next step. If voltage is not 5 volts, go to step 7).
5. Using test light connected to battery voltage, probe ground circuit of CKP sensor connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 8).
6. Reconnect CKP sensor connector. Using DVOM, backprobe CKP sensor signal circuit of PCM connector to ground. Crank engine. If voltage reading is 4 volts or greater, go to step 11). If voltage reading is less than 4 volts, go to step 10).
7. Turn ignition off. Disconnect PCM harness connector. Check 5-volt reference circuit for open, short to ground, or short to sensor ground circuit. Repair as necessary. After repairs, go to step 14). If circuits are okay, go to step 9).
8. Check for open or poor connections at sensor ground terminals of PCM. Repair as necessary. After repairs, go to step 14). If connections are okay, go to step 13).
9. Check for poor connections at 5-volt reference terminals of PCM. Repair terminals as necessary. After repairs, go to step 14). If terminals are okay, go to step 13).
10. Turn ignition off. Disconnect PCM harness connector. Check CKP sensor signal circuit for open, short to ground, or short to sensor ground circuit. Repair as necessary. After repairs, go to step 14). If circuits are okay, go to next step.
11. Check for poor connections at CKP sensor terminals of PCM. Repair terminals as necessary. After repairs, go to step 14). If terminals are okay, go to next step.
12. Replace CKP sensor. If CKP sensor is replaced, PCM must be programmed with new TDC offset. See the «ADJUSTMENTS - 6.5L DIESEL»(ref-20564) article. After replacing sensor, go to step 14).
13. Replace PCM. After replacing PCM, go to next step.
14. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0335. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
15. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

When PCM is in back-up fuel, long crank times, fast idle and poor performance conditions will exist. Check for poor connections at crankshaft position sensor and PCM. Intermittents could be caused by poor connections or wiring. When diagnosing intermittents, reproduce conditions under which failure occurs. Operate engine at a higher temperature and near RPM when problem occurs. Since heat and vibration often cause intermittents, operating engine at a higher temperature and near RPM when problem occurs could cause intermittent condition.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Turn ignition off. Disconnect optical/fuel temperature sensor connector. Turn ignition on, with engine off. Using DVOM, check voltage between 5-volt reference circuit of optical sensor connector and ground. If voltage is 5 volts, go to next step. If voltage is not 5 volts, go to step 5).
3. Using a test light connected to battery voltage, probe ground circuit of optical sensor connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 8).
4. Reconnect optical/fuel temperature sensor connector. Start and idle engine. Using scan tool, command engine speed to 900 RPM. Using DVOM on Hz scale, backprobe high resolution signal circuit of PCM. If DVOM reading is 3740-3940 Hz, go to step 11). If DVOM reading is not 3740-3940 Hz, go to step 10).
5. If vehicle is equipped with an electrical filter harness at the optical sensor, go to next step. If vehicle is not equipped with and electrical filter, go to step 7).
6. Remove electrical harness filter from vehicle. Using DVOM, check resistance of filter. If resistance is greater than 2 ohms, go to step 14). If resistance is less than 2 ohms, go to next step.
7. Turn ignition off. Leave electrical harness filter removed from vehicle. Disconnect PCM harness connector. Check 5-volt reference circuit for open, short to ground, or short to sensor ground circuit. Repair as necessary. After repairs, go to step 15). If circuit is okay, go to step 9).
8. Check for open or poor connections at sensor ground terminals of PCM. Repair as necessary. After repairs, go to step 14). If connections are okay, go to step 12).
9. Check for poor connections at 5-volt reference terminals of PCM. Repair terminals as necessary. After repairs, go to step 15). If terminals are okay, go to step 13).
10. Turn ignition off. Check for open or short to ground in high resolution signal circuit. Repair as necessary. After repairs, go to step 15). If circuit is okay, go to step 12).
11. Check for poor connections at high resolution signal terminals of PCM. Repair terminals as necessary. After repairs, go to step 15). If terminals are okay, go to step 13).
12. Replace injection pump. If fuel injection pump is replaced, new pump must be timed. See the «ADJUSTMENTS - 6.5L DIESEL»(ref-20564) article. After replacing injection pump, go to step 15).
13. Replace PCM. After replacing PCM, go to step 15).
14. Replace electrical filter. After replacing filter, go to next step.
15. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0370. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
16. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Fast idle and poor performance will exist when PCM is in back-up fuel. If DTC P0251 is also set, use scan tool on snapshot mode to properly identify fault. If air exists in fuel system (vehicle runs out of fuel), DTC could set.

Glow plug system assists in providing heat required to begin combustion during engine starting at cold ambient temperatures. Glow plugs are heated before and during cranking as well as initial engine operation. PCM controls glow plug on time by monitoring coolant temperatures and glow plug voltage.

DTC will set when the following conditions are present

1. PCM has commanded glow plugs on and voltage at glow plugs is less than 4 volts.

Or

1. PCM has commanded glow plugs off and voltage at glow plugs is greater than 4 volts.

Or

1. PCM has commanded glow plugs on and a greater than 2 volt difference exists between glow plug voltage and ignition voltage.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Turn ignition on, with engine off. Using a test light connected to ground, probe battery side of glow plug relay. If test light illuminates, go to next step. If test light does not illuminate, go to step 9).
3. Using scan tool, command glow plugs on. Observe GLOW PLUG SYSTEM display on scan tool. If scan tool displays glow plug value at 10-14 volts, go to next step. If scan tool does not display glow plug value at 10-14 volts, go to step 5).
4. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
5. Turn ignition off. Disconnect glow plug relay connector. Turn ignition on, with engine off. Using test light connected to ground, probe ignition feed circuit of glow plug relay connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 10).
6. Turn ignition on, with engine off. Connect test light between ignition feed circuit and ground circuit of glow plug relay connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 11).
7. Turn ignition on, with engine off. Leave glow plug relay connector disconnected. Using DVOM, probe control circuit of glow plug relay connector to ground. Using scan tool, command glow plugs on. If battery voltage is present, go to next step. If battery voltage is not present, go to step 12).
8. Reconnect glow plug relay connector. Turn ignition on, with engine off. Using test light connected to ground, probe glow plug side of glow plug relay connector. Using scan tool, command glow plugs on. If test light illuminates when glow plugs are commanded on, go to step 14). If test light does not illuminate when glow plugs are commanded on, go to step 16).
9. Check for poor connections at glow plug relay control terminal of PCM. Repair terminal as necessary. After repairs, go to step 18).
10. Repair open or short to ground in ignition feed circuit. After repairs, go to step 18).
11. Repair open or poor connections in ground circuit. After repairs, go to step 18).
12. Check for open or short to ground in control circuit. Repair as necessary. After repairs, go to step 18). If circuit is okay, go to next step.
13. Check for poor connections at glow plug relay control terminal of PCM. Repair terminal as necessary. After repairs, go to step 18). If terminals are okay, go to step 17).
14. Check for open or short to ground in signal circuit. Repair as necessary. After repairs, go to step 18). If circuit is okay, go to next step.
15. Check for poor connections at glow plug relay signal terminal of PCM. Repair terminal as necessary. After repairs, go to step 18). If terminals are okay, go to step 17).
16. Replace glow plug relay. After replacing relay, go to step 18).
17. Replace PCM. After replacing PCM, go to next step.
18. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0380. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
19. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Check for proper operation of glow plugs if glow plug relay is stuck on. When glow plugs are commanded on by scan tool, an internal PCM timer protects glow plugs from damage by cycling them on for 3 seconds then off for 12 seconds.

PCM operates a Pulse Width Modulated (PWM) solenoid to control EGR valve. This is a normally open solenoid. During normal operation, PCM compares desired MAF signal with the measured MAF signal and makes corrections in the duty cycle accordingly.

DTC will set when the following conditions are present

1. BARO reading at 75 kPa or greater.
2. Lowest achieved EGR pressure at full EGR is less than look up table value (internal to PCM).
3. MAF value is greater than or equal to 0.1484 g/cyl.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install vacuum gauge in place of EGR valve. Start engine and operate at idle. Apply parking brakes and block drive wheels. Place transmission in Drive. Observe vacuum gauge. If vacuum reading is 5-7 in. Hg, go to next step. If vacuum is not 5-7 in. Hg, to step 5).
3. Turn ignition off. Install a hand-held vacuum pump to EGR valve. Start and operate engine at idle, with transmission in Park. Using scan tool, observe cylinder air display while applying 15 in. Hg to EGR valve. If scan tool display reads a decrease of .10 g/cyl. or greater, go to next step. If reading does not indicate a decrease of .10 g/cyl. or greater, go to step 7).
4. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
5. Check vacuum source at solenoid assembly. If vacuum is 15 in. Hg, go to next step. If vacuum is not 15 in. Hg, go to step 8).
6. Check for restricted or leaky vacuum hose from solenoid to EGR valve. Repair as necessary. After repairs, go to step 9).
7. Replace EGR valve. After replacing EGR valve, go to step 9).
8. Repair vacuum pump. After repairs, go to next step.
9. After repairs, reset EGR Adaptive Learn Matrix (ALM) cells using scan tool. After resetting EGR ALM cells, go to next step.
10. Using scan tool, select CLEAR INFO. Start and warm engine to normal operating temperature. Test drive vehicle. Select DTC, SPECIFIC, then enter DTC P0404. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
11. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

The most likely cause of failure is a restricted vacuum line from the EGR valve to the vacuum "T" fitting.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Check if other EGR related DTCs are set. If other DTC(s) are present, diagnose affected DTC(s). If no other DTC(s) are present, go to next step.
3. Check for plugged EGR ports, exhaust system leaks or for exhaust modifications. Repair as necessary. After repairs, go to next step.
4. After repairs, reset EGR Adaptive Learn Matrix (ALM) using scan tool. After resetting EGR ALM, go to next step.
5. Using scan tool, select CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC that was set. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
6. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

The most likely cause of failure is a condition causing low backpressure.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Check if other EGR related DTCs are set. If other DTC(s) are present, diagnose affected DTC(s). If no other DTC(s) are present, go to next step.
3. Check for plugged EGR ports, exhaust system leaks or for exhaust modifications. Repair as necessary. After repairs, go to next step.
4. After repairs, reset EGR Adaptive Learn Matrix (ALM) using scan tool. After resetting EGR ALM, go to next step.
5. Using scan tool, select CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC that was set. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
6. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

The most likely cause of failure is a condition causing low backpressure.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install vacuum gauge in place of EGR control pressure/BARO sensor. Start and warm engine to normal operating pressure. Operate engine at idle. Observe vacuum gauge. If vacuum is 5-7 in. Hg, go to next step. If vacuum is not 5-7 in. Hg, go to step 4).
3. Repair restriction between EGR control pressure/BARO sensor and vacuum "T" fitting. After repairs, go to step 5).
4. Replace EGR control pressure/BARO sensor. After replacing sensor, go to next step.
5. After repairs, reset EGR Adaptive Learn Matrix (ALM) cells using scan tool. After resetting EGR ALM cells, go to next step.
6. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0404. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
7. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

A vacuum leak or pinched vacuum will cause DTC to set. Check all vacuum lines and components connected to hoses for leaks, sharp bends or deformities. Check vacuum source to EGR solenoid assembly. Check for leak in EGR valve and for proper vacuum line routing.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. With engine idling, observe EGR sensor voltage display on scan tool. If scan tool displays EGR sensor voltage at less than or equal to .24 volt, go to next step. If scan tool displays EGR sensor voltage at greater than .24 volt, go to step 5).
3. Turn ignition off. Disconnect EGR control pressure/BARO sensor connector. Connect a jumper wire between 5-volt reference circuit and signal circuit of EGR control pressure/BARO sensor harness connector. Turn ignition on. If scan tool displays EGR sensor voltage at greater than 4 volts, go to step 6). If scan tool displays EGR sensor voltage at less than 4 volts, go to next step.
4. Turn ignition off. Remove jumper wire. Using a test light connected to battery voltage, probe signal circuit of EGR control pressure/BARO sensor harness connector. Turn ignition on. If scan tool displays EGR sensor voltage at greater than 4 volts, go to step 9). If scan tool displays EGR sensor voltage at less than 4 volts, go to step 7).
5. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, diagnose affected DTC. Go to applicable DTC test.
6. Check for poor connection at EGR control pressure/BARO sensor. Repair as necessary. After repairs, go to step 12). If connection is okay, go to step 11).
7. Check for open in EGR control pressure/BARO sensor signal circuit. Repair as necessary. After repairs, go to step 12). If circuit is okay, go to next step.
8. Check for short to ground in EGR control pressure/BARO sensor signal circuit. Repair as necessary. After repairs, go to step 12). If circuit is okay, go to step 13).
9. Check for open in EGR control pressure/BARO sensor 5-volt reference circuit. Repair as necessary. After repairs, go to step 12). If circuit is okay, go to next step.
10. Check for short to ground in EGR pressure control/BARO sensor5-volt reference circuit. Repair circuit as necessary. After repairs, go to step 12). If circuit is okay, go to step 13).
11. Replace EGR control pressure/BARO sensor. After replacing sensor, go to step 14).
12. Repair circuit as necessary. After repairs, go to step 14).
13. Replace PCM. After replacing PCM, go to next step.
14. After repairs, reset EGR Adaptive Learn Matrix (ALM) cells using scan tool. After resetting EGR ALM cells, go to next step.
15. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0405. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
16. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

With ignition on and engine off, EGR pressure is equal to atmospheric pressure with signal voltage being high. Information is used by PCM as an indication of vehicle altitude. To test accuracy of a suspect sensor, compare reading with a known good vehicle. Reading should be the same plus or minus .4 volt. DTC will set if an intermittent open is present in signal circuit or 5-volt reference circuit.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Check if DTC P1653 is set. If DTC P1653 is set, go to DTC P1653 test. If DTC P1653 is not set, go to next step.
3. Install scan tool. With engine idling, observe EGR control pressure/BARO sensor voltage display on scan tool. If scan tool displays EGR control pressure/BARO sensor voltage greater than 4 volts, go to next step. If scan tool displays EGR control pressure/BARO sensor voltage less than 4 volts, go to step 5).
4. Turn ignition off. Disconnect EGR control pressure/BARO sensor connector. Turn ignition on. If scan tool displays EGR voltage less than one volt, go to step 6). If scan tool displays actual EGR voltage greater than one volt, go to step 10).
5. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
6. Ignition on, engine off. With DVOM connected to ground, probe 5-volt reference circuit at EGR connector. If voltage is greater than 5.2 volts, go to step 11). If not, go to next step.
7. Using a test light connected to battery voltage, probe ground circuit of EGR control pressure/BARO sensor connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 12).
8. Check for restriction in EGR vacuum source. If a problem was found, go to step 13). If a problem was not found, go to next step.
9. Replace EGR control pressure/BARO sensor. After replacing sensor, go to step 15).
10. Check for short to voltage in signal circuit. Repair as necessary. After repairs, go to step 13). If circuit is okay, go to step 14).
11. Check for short to voltage on 5-volt reference circuit and repair as necessary. After repairs, go to step 15). If circuit is okay, go to step 14).
12. Repair open in sensor ground circuit. After repairs, go to step 15).
13. Repair as necessary. After repairs, go to step 15).
14. Replace PCM. After replacing PCM, go to next step.
15. After repairs, reset EGR Adaptive Learn Matrix (ALM) using scan tool. After resetting EGR ALM, go to next step.
16. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0406. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
17. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

With ignition on and engine off, EGR pressure is equal to atmospheric pressure with signal voltage being high. Information is used by PCM as an indication of vehicle altitude. To test accuracy of a suspect sensor, compare reading with a known good vehicle. Reading should be same plus or minus .4 volt. DTC will set if open is present in ground circuit. If DTC is intermittent, see the TESTS W/O CODES article.

Speed sensor circuit consists of a magnetic, induction-type sensor, vehicle speed sensor buffer/module and wiring. Gear teeth pressed on output shaft induce an alternating current in sensor. Signal is transmitted to buffer. Buffer compensates for various axle ratios and converts signal into a square wave for use by speedometer, cruise control, anti-lock brakes and PCM. Buffer sends 2 different signals to PCM.

DTC will set when the following conditions are present

1. Vehicle speed is greater than 20 MPH.
2. Four wheel low is not selected.
3. VSS buffer calculated speed is less than half the transmission calculated speed.

Or

1. VSS buffer calculated speed is greater than transmission calculated speed by 20 MPH.
2. Conditions are met for 2 seconds.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. Raise drive wheels. With engine running, place transmission in any drive range. With drive wheels rotating, if vehicle speed increases when drive wheel speed increases, go to step 7). If vehicle speed does not increase when drive wheel speed increases, go to next step.
3. Place transmission in Park. Using a test light connected to ground, backprobe ignition feed circuit of VSS buffer/module connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 8).
4. Using test light, backprobe between ignition feed circuit and ground circuit of VSS buffer/module connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 9).
5. Using DVOM on AC scale, backprobe both VSS input circuits of VSS buffer/module connector to each other. Place transmission in any drive range with drive wheels rotating. If voltage increases as drive wheel speed increases, go to next step. If voltage does not increase as drive wheel speed increases, go to step 10).
6. If scan tool displays a trans output speed (MPH) increase with drive wheel speed increase, go to step 11). If trans output speed (MPH) reading does not change, go to step 13).
7. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
8. Repair open in ignition feed circuit. After repairs, go to step 15).
9. Repair open in ground circuit. After repairs, go to step 15).
10. Check for open or short to ground in complete VSS input circuit. After repairs, go to step 15).
11. Check for open or short to ground in VSS output circuit. Repair as necessary. After repairs, go to step 15). If circuit is okay, go to next step.
12. Check for poor connections at VSS output terminal of buffer/module and PCM. Repair as necessary. After repairs, go to step 15). If connections are okay, go to step 14).
13. Replace VSS buffer module. After replacing module, go to step 15).
14. Replace PCM. After replacing PCM, go to next step.
15. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0501. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
16. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Check connections at VSS buffer/module and PCM. If DTC P0722 or DTC P0723 is set, see AUTO TRANS DIAGNOSIS article in the AUTOMATIC TRANSMISSION section.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. Turn ignition on, with engine off. Turn cruise switch off. If scan tool displays resume switch is on, go to next step. If scan tool does not display that resume switch is on, go to step 4).
3. Turn ignition off. Disconnect PCM harness connector. Turn ignition on. Using a test light connected to ground, probe resume switch signal circuit at PCM harness connector. If test light illuminates, go to step 5). If test light does not illuminate, go to step 6).
4. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
5. Repair short to voltage in resume switch signal circuit. After repairs, go to step 7).
6. Replace PCM. After replacing PCM, go to next step.
7. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0567. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
8. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Check for resume/accel switch stuck in engage position or signal circuit shorted to voltage.

Cruise Control System Diagram. Scheme 22

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. Turn ignition on, with engine off. Turn cruise switch off. If scan tool displays set switch is on, go to next step. If scan tool does not display that set switch is on, go to step 4).
3. Turn ignition off. Disconnect PCM harness connector. Turn ignition on. Using a test light connected to ground, probe set switch signal circuit of PCM connector. If test light illuminates, go to step 5). If test light does not illuminate, go to step 6).
4. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
5. Check for short to voltage in set switch signal circuit or set switch stuck in ON position. Repair as necessary. After repairs, go to step 8).
6. Replace PCM. After replacing PCM, go to next step.
7. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0568. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
8. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Check for set/coast switch stuck in engage position or signal circuit shorted to voltage.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. Turn ignition on, with engine off. Apply brakes. If scan tool displays cruise brake switch closed, then open when brakes are released, go to next step. If scan tool does not display cruise brake switch closed then open when brakes are released, go to step 4).
3. Apply brakes again. If scan tool displays cruise brake switch open, then closed when brakes are released, go to step 8). If scan tool does not display cruise brake switch open, then closed when brakes are released, go to step 6).
4. Turn ignition off. Disconnect brakelight switch connector. Turn ignition on, with engine off. Using a test light connected to ground, probe normally open feed circuit (terminal "B") of brake light switch connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 9).
5. Disconnect brakelight switch connector. Connect a jumper wire between normally open feed circuit and normally open signal circuit of brakelight switch connector. If scan tool displays cruise brake switch closed, go to next step. If scan tool does not display cruise brake switch closed, go to step 10).
6. Disconnect brakelight switch connector. Turn ignition on, with engine off. Using a test light connected to ground, probe normally closed feed circuit of brake light switch connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 12).
7. Disconnect brakelight switch connector. Connect a jumper wire between normally closed feed circuit and normally closed signal circuit of brakelight switch connector. If scan tool displays cruise brake switch closed, go to step 15). If scan tool does not display cruise brake switch closed, go to step 14).
8. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
9. Check for open or short to ground in normally open feed circuit. Repair as necessary. After repairs, go to step 17).
10. Check for open or short to ground in normally open signal circuit. Repair as necessary. After repairs, go to step 17). If circuit is okay, go to next step.
11. Check for poor connection at normally open signal terminal of PCM. Repair as necessary. After repairs, go to step 17). If connection is okay, go to step 16).
12. Check for open or short to ground in normally closed feed circuit. Repair as necessary. After repairs, go to step 17).
13. Check for open or short to ground in normally closed signal circuit. Repair as necessary. After repairs, go to step 17). If circuit is okay, go to next step.
14. Check for poor connection at normally closed signal terminal of PCM. Repair as necessary. After repairs, go to step 17). If connection is okay, go to step 16).
15. Replace brakelight switch. After replacing switch, go to step 17).
16. Replace PCM. After replacing PCM, go to next step.
17. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0571. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
18. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

See the TESTS W/O CODES article. Check customer driving habits and/or unusual traffic conditions (i.e., stop and go, expressway traffic).

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Replace PCM. After replacing PCM, go to next step.
3. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0601. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
4. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Check all PCM connections. Repair as necessary. After repairs, go to step 4). If connections are okay, go to next step.
3. Replace PCM. After replacing PCM, go to next step.
4. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0602. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
5. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Check all PCM connections. Repair as necessary. After repairs, go to step 4). If connections are okay, go to next step.
3. Replace PCM. After replacing PCM, go to next step.
4. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0604. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
5. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Check if DTC P0370 is set. If DTC P0370 is set, go to DTC P0370 test. If DTC P0370 is not set, go to next step.
3. Replace PCM. After replacing PCM, go to next step.
4. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0606. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
5. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Turn ignition off. Disconnect APP sensor connector. Turn ignition on, with engine off. Using DVOM, check voltage between all 5-volt reference circuits of APP sensor connector and ground. If voltage is less than 4.8 volts, go to step 4). If voltage is greater than 4.8 volts, go to next step.
3. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
4. Turn ignition off. Disconnect PCM harness connector. Check for short to ground in 5-volt reference circuit. Repair as necessary. If 5-volt reference circuit is shorted to ground, go to step 6). If 5-volt reference circuit is not shorted to ground, go to next step.
5. Replace PCM. After replacing PCM, go to next step.
6. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1125. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
7. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

DTC P1125 will set along with multiple APP DTCs. Diagnose all other APP DTCs first.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Check if any other EGR related DTC(s) are present. If other DTC(s) are present, diagnose using applicable DTC. If no other DTC(s) are present, go to next step.
3. Check for air inlet duct leaks (after MAF sensor) or intake manifold gasket leak. Repair as necessary. After repairs, go to next step.
4. After repairs, reset EGR Adaptive Learn Matrix (ALM) cells using scan tool. After resetting EGR ALM cells, go to next step.
5. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1125. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
6. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Failure is most likely caused by a leaky intake duct after the MAF sensor.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. If scan tool displays a TDC offset greater than 2.5 or less than -2.5, go to step 4). If scan tool does not display a TDC offset greater than 2.5 or less than -2.5, go to next step.
3. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
4. Check if any other DTCs are set. If any other DTCs are set, go to appropriate DTC. If any other DTCs are not set, go to next step.
5. Clear all DTCs and reset injection timing until TDC offset is -.25 to -.75. See the «ADJUSTMENTS - 6.5L DIESEL»(ref-20564) article. If timing is -.25 to -.75, go to step 7). If timing is not -.25 to -.75, go to next step.
6. Check crankshaft position sensor for proper installation or loose or broken sensor mounting tab. Repair as necessary. After repairs, go to step 8). If no repairs are required, go to next step.
7. Replace PCM. After replacing PCM, go to next step.
8. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1214. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
9. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Check if DTC P0219 is set. If DTC P0219 is set, go to DTC P0219 test. If DTC P0219 is not set, go to next step.
3. Check if engine starts. If engine starts, go to next step. If engine does not start, go to step 7).
4. Start and warm engine to normal operating temperature. Using scan tool, observe injection pump closure time. If scan tool displays injection pump closure time at less than .75 millisecond, go to next step. If scan tool displays injection pump closure time at greater than .75 millisecond, go to step 6).
5. With engine running, observe injection pump closure time on scan tool. If scan tool displays injection pump closure time as 0.0 milliseconds, go to step 8). If scan tool does not display injection pump closure time as 0.0 millisecond, go to step 10).
6. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
7. Check for open in closure ground circuit. Repair as necessary. After repairs, go to step 12).
8. Check for open or short to ground in closure signal circuit. Repair as necessary. After repairs, go to step 12). If circuit is okay, go to next step.
9. Check for poor connection at closure signal terminal of PCM. Repair terminal as necessary. After repairs, go to step 12). If terminal connection is okay, go to next step.
10. Replace fuel injection pump. If fuel injection pump is replaced, new pump must be timed. See the «ADJUSTMENTS - 6.5L DIESEL»(ref-20564) article. After replacing injection pump, go to step 12).
11. Replace PCM. After replacing PCM, go to next step.
12. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1216. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
13. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

If any other DTCs are set with DTC P1216, diagnose other DTCs first. If vehicle is running close to DTC setting closure time, vehicle should be checked during cold start-ups and during hot conditions.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Check if DTC P0370 is set. If DTC P0370 is set, go to DTC P0370. If DTC P0370 is not set, go to next step.
3. Start and warm engine to normal operating temperature. Using scan tool, observe injection pump closure time. If scan tool displays injection pump closure time greater than 2.4 milliseconds, go to next step. If scan tool displays injection pump closure time less than 2.4 millisecond, go to step 5).
4. Turn on all accessories. Engine idling. Using DVOM connected to ground, check voltage at FUEL SOL fuse (fuel solenoid driver ignition feed circuit) in underhood relay center. If voltage is 11-16 volts, go to step 7). If not, go to step 6).
5. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
6. Check fuel solenoid driver ignition feed circuit for poor connections or aftermarket add-ons. Repair as necessary. After repairs, go to step 8).
7. Replace fuel injection pump. If fuel injection pump is replaced, new pump must be timed. See the «ADJUSTMENTS - 6.5L DIESEL»(ref-20564) article. After replacing injection pump, go to next step.
8. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1217. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
9. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

A weak (mechanical failure) fuel solenoid will cause DTC P1217 to set. If any other DTCs are set with DTC P1217, diagnose other DTCs first. If vehicle is running close to DTC setting closure time, vehicle should be checked during cold start-ups and during hot conditions.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Check if any other DTCs are set. If any other DTCs are set, go to appropriate DTC. If any other DTCs are not set, go to next step.
3. Check connection at fuel solenoid driver. Clear DTCs and cycle engine. If DTC clears, go to step 5). If DTC does not clear, go to next step.
4. Replace fuel injection pump. If fuel injection pump is replaced, new pump must be timed. See the «ADJUSTMENTS - 6.5L DIESEL»(ref-20564) article. After replacing injection pump, go to next step.
5. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
6. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1218. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
7. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Check connection at fuel injector driver. Clear DTCs and cycle engine. If DTC clears, treat condition as an intermittent.

1. Capture and record freeze frame and failure records data. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Check if any other DTCs are set. If any other DTCs are set, go to appropriate DTC. If any other DTCs are not set, go to next step.
3. Check for restriction in vacuum line from EGR valve to vacuum "T" fitting. Check for faulty EGR valve. Repair or replace as necessary. After repairs, go to next step.
4. After repairs, reset EGR Adaptive Learn Matrix (ALM) cells using scan tool. After resetting EGR ALM cells, go to next step.
5. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1406. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
6. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

A vacuum leak will cause DTC P1406 to set. Check all vacuum lines and components connected to hoses for leaks or deformities. Check vacuum source to EGR solenoid assembly or EGR valve. Check for proper vacuum hose routing.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install vacuum gauge in place of EGR valve. Start engine and operate at idle. Apply parking brakes and block drive wheels. Place transmission in Drive. Observe vacuum gauge. If vacuum reading is 5-7 in. Hg, go to step 4). If vacuum is not present, to next step.
3. Turn ignition off. Disconnect vacuum hose to EGR vent solenoid. Install vacuum gauge to EGR vent solenoid hose. Start and operate engine at idle, with transmission in Drive. Observe vacuum gauge. If vacuum is present, go to step 7). If is not present, go to step 5).
4. Turn ignition off. Install a hand-held vacuum pump to EGR valve. Apply 15 in. Hg to EGR valve. If EGR valve holds vacuum, go to step 6). If EGR valve does not hold vacuum, go to step 11).
5. Check main vacuum source at solenoid assembly. If vacuum reading is greater than or equal to 15 in. Hg, go to step 10). If vacuum reading is less than 15 in. Hg, go to step 8).
6. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
7. Check for restricted or leaky vacuum hose from solenoid to EGR valve. Check for faulty EGR vent solenoid. Repair as necessary. After repairs, go to step 12). If vacuum hoses or EGR vent solenoid are okay, go to step 10).
8. Check for leaking or deformed vacuum hose to vacuum pump. Repair as necessary. After repairs, go to step 12).
9. Replace vacuum pump. After replacing vacuum pump, go to step 12).
10. Repair leaking or deformed vacuum hoses at EGR solenoid, or faulty EGR solenoid. Repair or replace as necessary. After repairs, go to step 12).
11. Replace EGR valve. After replacing EGR valve, go to next step.
12. After repairs, reset EGR Adaptive Learn Matrix (ALM) cells using scan tool. After resetting EGR ALM cells, go to next step.
13. Using scan tool, select CLEAR INFO. Start and warm engine to normal operating temperature. Test drive vehicle. Select DTC, SPECIFIC, then enter DTC P1409. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
14. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

A vacuum leak will cause DTC P1409 to set. Check all vacuum lines and components connected to hoses for leaks or deformities. Check vacuum source to EGR solenoid assembly or EGR valve. Check for proper vacuum hose routing.

1. Capture and record freeze frame and failure records data. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Replace PCM. After replacing PCM, go to next step.
3. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1621. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
4. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test. If no other DTC(s) are displayed, system is okay.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Replace PCM. After replacing PCM, go to next step.
3. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1627. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
4. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. Start engine or crank engine for 15 seconds if engine does not start. Check if DTC P1635 sets. If DTC P1635 sets, go to next step. If DTC P1635 does not set, go to step 5).
3. Turn ignition off. Disconnect boost sensor connector. Turn ignition on, with engine off. Using DVOM, probe 5-volt reference circuit of boost sensor connector. If voltage is less than 4 volts, go to next step. If voltage is greater than 4 volts, go to step 6).
4. Turn ignition off. Disconnect PCM connector. Using test light, probe boost sensor 5-volt reference circuit of PCM connector to battery voltage. If test light illuminates, go to step 7). If test light does not illuminate, go to step 8).
5. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
6. Replace boost sensor. After replacing sensor, go to step 9).
7. Repair short to ground in 5-volt reference circuit. After repairs, go to step 9).
8. Replace PCM. After replacing PCM, go to next step.
9. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1635. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
10. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

During the time failure is present, setting of additional DTCs that share a 5-volt reference may also set.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. Turn ignition on, with engine off. Turn MIL on and off using scan tool. If MIL illuminates, go to next step. If MIL does not illuminate, go to step 4).
3. DTC is intermittent. If other DTC(s) exist, go to that DTC for diagnosis. If no other DTC(s) exist, see DIAGNOSTIC AIDS.
4. Turn ignition off. Disconnect PCM harness connector. Turn ignition on, with engine off. If MIL illuminates, go to next step. If MIL does not illuminate, go to step 7).
5. Ignition on, engine off. Using a fused jumper wire, jumper PCM connector MIL driver circuit terminal to ground. If MIL illuminates, go to next step. If MIL does not illuminate, go to step 8).
6. Check for poor connections at PCM. If problem was found, repair as necessary. After repairs, go to step 10). If connections are okay, go to step 9).
7. Repair short to ground in MIL control circuit. Repair as necessary. After repairs, go to step 10).
8. Check for the following conditions in MIL control circuit: Open ignition feed. Poor connections at PCM. Faulty bulb. Control circuit open or shorted to battery voltage. After repairs, go to step 10).
9. Replace PCM. After replacing PCM, go to next step.
10. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1641. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
11. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

A faulty bulb or short to ground in MIL control circuit will cause DTC P1641 to set.

Instrument Cluster Diagram. Scheme 23

The WAIT TO START light is illuminated by the PCM when the glow plugs are commanded on. When the PCM is commanding the WAIT TO START light on, the voltage potential of the circuit will be low (near zero volts). The the PCM is commanding the WAIT TO START light off, the voltage potential of the circuit will be high (near battery voltage).

The primary function of the PCM is supply ground to the WAIT TO START light circuit.

DTC will set when the following conditions are present

1. WAIT TO START light is requested on.
2. Voltage to WAIT TO START light circuit is high (near battery voltage).

Or

1. WAIT TO START light is requested off.
2. Voltage to WAIT TO START light control circuit is low (near zero volts).

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Turn ignition on, with engine off. Using scan tool, command glow plug system on. If WAIT TO START light illuminates, go to next step. If WAIT TO START light does not illuminate, go to step 4).
3. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
4. Turn ignition off. Disconnect PCM harness connector containing the WAIT TO START light control circuit. Turn ignition on, with engine off. If WAIT TO START light illuminates, go to step 7). If WAIT TO START light does not illuminate, go to next step.
5. Using a fused jumper wire connected to ground, probe light control circuit in PCM harness connector. If WAIT TO START light illuminates, go to next step. If WAIT TO START light does not illuminate, go to step 8).
6. Check connections at PCM. Repair as necessary. After repairs, go to step 10). If connections are okay, go to step 9).
7. Check for short in WAIT TO START control circuit. Repair as necessary. After repairs, go to step 10).
8. Check WAIT TO START circuit for open ignition feed to bulb, faulty bulb or control circuit that is open or shorted to voltage. Repair as necessary. After repairs, go to step 10).
9. Replace PCM. After replacing PCM, go to next step.
10. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1641. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
11. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

A faulty bulb or short to ground in WAIT TO START control circuit will cause DTC to set.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. Turn ignition on, with engine off. Using scan tool, command EGR vent solenoid on and off, and listen for an audible click. If solenoid turns on and off, go to next step. If solenoid does not turn on and off, go to step 5).
3. Turn ignition off. Disconnect PCM harness connector containing the EGR vent solenoid circuit. Turn ignition on. Using DVOM in the 10-amp scale, check current between solenoid control circuit in the PCM harness connector to ground for 2 minutes. If current draw is less than .75 amp., but not zero, go to step 8). If current draw is greater than .75 amp., go to next step.
4. Turn ignition off. With PCM harness connector still disconnected, disconnect EGR vent solenoid harness connector. Using DVOM, check resistance from solenoid control circuit in PCM harness connector to ground. If resistance is infinite, go to step 13). If resistance is not infinite, go to step 10).
5. Disconnect EGR vent solenoid. Turn ignition on, with engine off. Using a test light, connect test light between EGR vent solenoid harness connectors. Using scan tool, command EGR solenoid on and off. If test light illuminates with each command, go to step 9). If test light does not illuminate with each command, go to next step.
6. Turn ignition on, with engine off. Using test light connected to ground, probe the EGR vent solenoid ignition feed circuit. If test light illuminates, go to next step. If test light does not illuminate, go to step 12).
7. Turn ignition off. Reconnect EGR vent solenoid harness connector. Disconnect PCM harness connector containing the solenoid control circuit. Turn ignition on. Using a fused jumper wire connected to ground, probe solenoid control circuit at PCM harness connector. If EGR vent solenoid operates, go to step 11). If solenoid does not operate, go to step 10).
8. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, diagnose affected DTC. Go to applicable DTC test.
9. Check for poor connection at EGR vent solenoid. Repair as necessary. After repairs, go to step 15). If connection is okay, go to step 13).
10. Repair EGR control circuit. Repair as necessary. After repairs, go to step 15).
11. Check for poor connection at PCM and EGR vent solenoid. Repair as necessary. After repairs, go to step 15). If circuit is okay, go to step 14).
12. Repair open in ignition feed circuit. After repairs, go to step 15).
13. Replace EGR vent solenoid. After replacing solenoid, go to step 15).
14. Replace PCM. After replacing PCM, go to next step.
15. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1653. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
16. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Scan tool has a 5 second ON time. The EGR vent solenoid can be commanded on and off for as many times as needed in 5 second intervals. Other EGR related DTC(s) may set with this DTC. A quick operational check can be made by commanding the EGR vent solenoid on and off with the scan tool while monitoring actual EGR. Actual EGR will display BARO when EGR solenoid is off.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Turn ignition on, with engine off. Using scan tool, command light on and off. If light turns on and off, go to next step. If not, go to step 4).
3. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
4. Ignition off. Unplug PCM harness connector containing the light control circuit. Turn ignition on, with engine off. If light is on, go to next step. If not, go to step 7).
5. With fused jumper wire to ground, probe light control driver circuit at PCM connector. If light is on, go to next step. If not, go to step 8).
6. Check for poor PCM connections. Repair as necessary. After repairs, go to step 10). If connections are okay, go to step 9).
7. Repair short to ground in SERVICE THROTTLE SOON indicator light control circuit. After repairs, go to step 10).
8. Check for the following conditions in SERVICE THROTTLE SOON indicator light control circuit: Open ignition feed circuit to bulb. Faulty bulb. Faulty fuse. After repairs, go to step 10).
9. Replace PCM. After replacing PCM, go to next step.
10. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1654. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
11. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

A faulty bulb or short to ground in SERVICE THROTTLE SOON indicator light control circuit will cause DTC P1654 to set.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Install scan tool. Start and idle engine. Using scan tool, command EGR solenoid on and off. If actual EGR responds to scan tool commands, go to step 5). If actual EGR does not respond to scan tool commands, go to next step.
3. Turn ignition off. Unplug PCM harness connector containing EGR solenoid control circuit. Turn ignition on. With DVOM connected to ground, set DVOM on 10-amp scale, check current from PCM connector EGR solenoid control circuit terminal. If current draw is less than .75 amp (but not zero), go to step 8). If current is not less than .75 amp (or is zero), go to next step.
4. Turn ignition off. With PCM connector still unplugged, unplug EGR solenoid connector. Check resistance between ground and PCM connector EGR solenoid control circuit terminal. If resistance is infinite, go to step 13). If not, go to step 10).
5. Turn ignition off. Disconnect EGR solenoid connector. Turn ignition on, with engine off. Connect test light between control circuit and ignition feed circuit of EGR solenoid connector. If test light illuminates, go to step 9). If test light does not illuminate, go to next step.
6. Turn ignition on, with engine off. Using test light connected to ground, probe ignition feed circuit of EGR solenoid connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 12).
7. Turn ignition off. Reconnect EGR solenoid. Unplug PCM connector containing EGR solenoid control circuit. Turn ignition on. Using a fused jumper wire connected to ground, probe PCM connector EGR solenoid control circuit terminal. If solenoid clicks, go to step 11). If not, go to step 10).
8. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
9. Check for poor connections at EGR solenoid. Repair terminals as necessary. After repairs, go to step 15). If terminals are okay, go to step 13).
10. Repair EGR solenoid control circuit. After repairs, go to step 15).
11. Check for poor connection at EGR solenoid control terminal of PCM. Repair as necessary. After repairs, go to step 15). If connections are okay, go to step 14).
12. Repair open in ignition feed circuit. After repairs, go to step 15).
13. Replace EGR solenoid. After replacing solenoid, go to step 15).
14. Replace PCM. After replacing PCM, go to next step.
15. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1655. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
16. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Scan tool has a 5 second on time abort. EGR solenoid can be commanded on as many times as needed in 5 second intervals. Other EGR DTCs may also set when DTC P1655 is set. This diagnostic can be checked at key up. A quick operational check may be performed by commanding EGR solenoid on and off using scan tool while monitoring actual EGR. Actual EGR will display BARO (approximately) when EGR solenoid is off. Full EGR will be achieved when EGR solenoid is commanded on using scan tool.

1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the «BASIC TESTING - 6.5L DIESEL»(ref-20661) article. Then go to next step.
2. Turn ignition on, with engine off. Using scan tool, command wastegate solenoid on and off and listen for an audible click. If solenoid turns on and off, go to next step. If solenoid does not turn on and off, go to step 5).
3. Turn ignition off. Unplug PCM harness connector containing wastegate solenoid control circuit. Turn ignition on. Using DVOM connected to ground, set DVOM on 10-amp scale and check current from PCM connector wastegate solenoid control circuit terminal. If current draw is less than .75 amp (but not zero), go to step 8). If current is not less than .75 amp (or is zero), go to next step.
4. Turn ignition off. With PCM harness connector still unplugged, unplug wastegate solenoid connector. Check resistance between ground and PCM connector EGR solenoid control circuit terminal. If resistance is infinite, go to step 13). If not, go to step 10).
5. Turn ignition off. Disconnect wastegate solenoid connector. Turn ignition on, with engine off. Connect test light between control circuit and ignition feed circuit of wastegate solenoid connector. If test light illuminates, go to step 9). If test light does not illuminate, go to next step.
6. Turn ignition on, with engine off. Using test light connected to ground, probe ignition feed circuit of wastegate solenoid connector. If test light illuminates, go to step 7). If test light does not illuminate, go to step 12).
7. Turn ignition off. Reconnect solenoid. Unplug PCM harness connector containing wastegate solenoid control circuit. Turn ignition on. With fused jumper wire connected to ground, probe PCM connector wastegate solenoid control circuit terminal. If solenoid clicks, go to step 11). If not, go to step 10).
8. DTC is intermittent. If additional DTC(s) are set, diagnose those DTC(s). If no DTC(s) are set, see DIAGNOSTIC AIDS.
9. Check for poor connections at wastegate solenoid. Repair terminals as necessary. After repairs, go to step 15). If connections are okay, go to step 13).
10. Repair wastegate solenoid control circuit. After repairs, go to step 15).
11. Check for poor connection at wastegate solenoid control terminal of PCM. Repair as necessary. After repairs, go to step 15). If connection is okay, go to step 14).
12. Repair open in ignition feed circuit. After repair, go to step 15).
13. Replace wastegate solenoid. After replacing solenoid, go to step 15).
14. Replace PCM. After replacing PCM, go to next step.
15. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1656. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
16. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

This diagnostic will set when control circuit does not follow PCM command (when solenoid is requested on, voltage will drop; when solenoid is requested off, ignition voltage will be present). Scan tool has a 5 second on time abort. Wastegate solenoid can be commanded on as many times as needed in 5 second intervals. DTC P0236 may also set when DTC P1656 is set. This diagnostic can be checked at key up. Engine will not respond to scan tool commands at idle (engine unable to achieve boost pressures greater than BARO at idle) or at any engine speed greater than idle (PCM control abort to prevent engine damage).