Engine Controls - Tests W/codes - 6.5l Diesel GMC Suburban I

INTRODUCTION

The 6.5L Diesel Electronic Control (DEC) system, electronically controls EGR system operation, Torque Converter Clutch (TCC) engagement, fuel control and fuel injection timing and is controlled by the Powertrain Control Module (PCM).

On diesel models with 4L60-E electronically-controlled transmission, transmission is controlled by the PCM. All other diesel models with 4L80-E electronically-controlled transmission, transmission are controlled by the PCM. TCM only controls the electronic transmission and no other components.

The PCM/TCM monitors a number of transmission functions and uses the data to control shift solenoids, TCC, and pressure control solenoid to regulate upshift pattern, downshift pattern and line pressure (shift quality).

Most engine/transmission control problems are NOT computer related, but result from mechanical breakdowns, poor electrical connections, or damaged vacuum hoses. Before condemning the computer system, carefully perform visual and mechanical inspections covered in BASIC TESTING - 6.5L DIESEL article. Failure to perform these inspections can result in lost diagnostic time.

If no faults were found while performing visual and mechanical inspections in BASIC TESTING - 6.5L DIESEL article, go to DIAGNOSTIC PROCEDURE under SELF-DIAGNOSTIC SYSTEM. If no diagnostic trouble codes or only a non-running DTC 12 is present and driveability problems exist, proceed to TESTS W/O CODES - 6.5L DIESEL article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.). If only intermittent codes are present, see INTERMITTENTS in TESTS W/O CODES - 6.5L DIESEL article.

TRANSMISSION APPLICATIONS

SELF-DIAGNOSTIC SYSTEM

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

Note. Unless specifically stated otherwise, references to PCM also apply to TCM-equipped vehicles.

The 6.5L DEC/electronically-controlled transmission systems 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/TCM will illuminate the Malfunction Indicator Light (MIL) located on instrument cluster. When malfunction is detected and light is turned on, a corresponding Diagnostic Trouble Code (DTC) will be stored in PCM/TCM memory. To retrieve stored codes, 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 appropriate ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK chart. After any DEC/electronically-controlled transmission systems repair, repeat On-Board Diagnostic (OBD) system check.

Diagnostic Procedure

1. Ensure all non-controlled systems NOT related to the Diesel Electronic Control (DEC)/electronically-controlled transmission systems are operating properly. DO NOT proceed with testing unless all non-DEC/electronically-controlled transmission systems problems are repaired.
2. ALWAYS begin diagnosis with On-Board Diagnostic (OBD) system check to determine if DEC/electronically-controlled transmission systems and PCM/TCM are working properly. See appropriate ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK chart. If trouble codes, other than Diagnostic Trouble Code (DTC) 12 are displayed, determine if they are hard or intermittent trouble codes.
3. A hard code is present while 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 «TESTS W/O CODES - 6.5L DIESEL»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-tests-wo-codes-65l-diesel) article.

ENTERING & EXITING DIAGNOSTIC MODE

1. With ignition on and engine off, connect a jumper wire between Data Link Connector (DLC) terminal "B" (diagnostic terminal) and terminal "A" (ground). (Scheme 112) The Diesel Electronic Control (D EC)/electronically-controlled transmission systems will enter diagnostic mode.
2. In this mode, PCM/TCM will display DTC 12 by flashing the MIL once, followed by a short pause, then 2 flashes in quick succession.
3. DTC 12 will be displayed 3 times. If no other codes are stored, DTC 12 will continue to flash until diagnostic terminal is ungrounded. To exit diagnostic mode, turn ignition off and remove jumper from DLC.

Scheme 112

TROUBLE CODE IDENTIFICATION

Note. Trouble codes retrieved from PCM may be either engine or transmission related. Trouble codes retrieved from TCM are only transmission related. Both engine and transmission related codes are covered in this article. See the DTC IDENTIFICATION to determine if code is engine or transmission related.

1. The DEC/electronically-controlled transmission systems codes indicate failure of a specific sensor and/or circuit. Sensor/circuit diagnosis may indicate replacement of PCM/TCM. DTC 51 indicates PROM is either improperly installed or has failed.
2. If PCM/TCM is replaced at any point during diagnostic testing and if condition is still not corrected after replacing PCM/TCM, the following may be the cause: An incorrect PCM/TCM or PROM application may cause a malfunction, which may or may not set a code. The PCM/TCM connector may be the problem. Connector terminals may have to be removed from connector to be checked properly. PROM failure. Although the PROM rarely fails, it could be the cause of the problem. Replacement PCM/TCM may be faulty. Intermittent problem. Make a careful physical inspection of affected sensor/circuit. A shorted solenoid, coil relay, or harness may be the cause of PCM/TCM failure. Use Short Circuit Tester (J-34636) to check for short circuits.

DTC IDENTIFICATION

CLEARING TROUBLE CODES

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

Diagnostic trouble codes should be cleared after repairs have been completed. Also, some diagnostic charts require codes to be cleared before using diagnostic chart.

1. To clear codes, use Tech 1 scan tester. If scan tester is not available, perform the following procedure. With ignition off, connect a jumper wire between Data Link Connector (DLC) terminal "B" (diagnostic terminal) and terminal "A" (ground). (Scheme 112) Turn ignition on. Fully apply brake pedal, then fully apply accelerator pedal.
2. Check MIL for DTC 12. Release brake pedal, then release accelerator pedal. Check MIL again for DTC 12. Remove jumper wire from DLC. Turn ignition off. If no hard fault codes are present (only intermittent codes exist), proceed to «TESTS W/O CODES - 6.5L DIESEL»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-tests-wo-codes-65l-diesel) article for intermittent diagnostic procedures.

PCM/TCM LOCATION

PCM is located behind right side of dash.

SPECIAL TOOLS (DIAGNOSTIC)

Special scan testers, plugged into the DLC, may be used to read trouble codes, and check voltages in system on serial data line. These testers can save a great deal of time. For additional information, see owner's manual included with tester.

SCAN TESTER USAGE

Note. Before connecting scan tester, check diagnostic system and ensure accurate information is received by scan tester. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. If vehicle does not pass On-Board Diagnostic (OBD) system check, information received by scan tester may be invalid.

The scan tester is a specialized tester 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 testers reduce diagnostic time by furnishing input data (voltage signals) which can be compared to specification parameters. See appropriate TYPICAL TECH 1 DATA VALUES table.

Scan testers 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/TCM. They do not indicate whether devices respond properly to that signal. This must be verified at output device using a voltmeter or test light.

Note. DTC 12 should always exist when DLC test terminal is grounded with key on and engine off, but it may not be indicated by all makes of scan tester.

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

Note. Information obtained by scan tester is only as accurate as the tester itself. If erroneous voltage signals are suspected, verify tester information using a digital voltmeter and wiring schematic. If non-existent codes are displayed, turn ignition off and remove tester. Turn ignition on and ground DLC test terminal. If same codes are not flashed by Malfunction Indicator Light (MIL) as were indicated by scan tester, tester cannot be used on vehicle and information obtained by it will not be guaranteed accurate.

TYPICAL TECH 1 DATA VALUES

Note. Information contained in the following table is typical of readings taken on vehicle with engine idling, lower radiator hose hot, throttle closed, transmission in Park or Neutral, closed loop status achieved and all accessories off (except as noted in tables). Not all devices and systems are used on all models. For additional information, see tester owner's manual.

TYPICAL TECH-1 DATA VALUES

TYPICAL TECH 1 DATA VALUES (TRANSMISSION)

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 tester may also be used to access data parameters. Tester will supply a visual reading of most inputs, and some outputs, to PCM/TCM.

DIAGNOSTIC TROUBLE CODE CHARTS

Note. The following figures are courtesy of General Motors Corp.

ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK (MODELS WITH PCM)

The On-Board Diagnostic (OBD) system check is an organized approach to identifying a problem created by a control module system malfunction. This is the starting point for any driveability complaint diagnosis, as it directs technician to the next logical step in diagnosis, helps reduce diagnostic time and prevents the unnecessary replacement of good parts.

Note. Test numbers refer to numbers on diagnostic chart.

1. This tests MIL operation. With ignition on and engine off, light should be on.
2. This step will isolate if customer complaint is a MIL or driveability problem.
3. Although the control module is powered up, a symptom could exist because of a system fault.
4. Use Tech-1 to aid in diagnosis (to check if serial data is available). If a PROM error is present, the PCM may have been able to flash DTC 12 or 51, but not enable serial data.
5. Although the control module is powered up, a "CRANKS BUT WILL NOT RUN" symptom could exist because of a PCM or system fault.
6. This step will isolate if customer complaint is a MIL or driveability problem with no MIL displayed. Proceed to the «DTC IDENTIFICATION»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-tests-wcodes-65l-diesel) under TROUBLE CODE IDENTIFICATION, to determine if code is valid. An invalid DTC may be the result of a faulty scan tester, PROM or PCM.
7. Comparison of actual control system data with typical scan tester data values is a quick check to determine if any parameter is not within limits. A base engine problem (i.e. advanced cam timing) may substantially alter sensor values. See appropriate TYPICAL TECH 1 DATA VALUES table in introduction.

OBD System Check Schematic (6.5L Diesel) On-Board Diagnostic (OBD) System Check (Models With PCM). Scheme 113

OBD System Check Flow Chart (6.5L Diesel) On-Board Diagnostic (OBD) System Check (Models With PCM). Scheme 114

CHART A-1, NO MIL (SERVICE ENGINE SOON LIGHT) (MODELS W/ PCM)

MIL should be on when engine is off and ignition is on. Switched battery voltage is supplied to MIL. The PCM turns light on by providing a ground path through the MIL (SERVICE ENGINE SOON) control circuit.

Note. Test numbers refer to numbers on diagnostic chart.

1. If fusible link or ECM-B fuse is blown, see «WIRING DIAGRAMS»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-tests-wcodes-65l-diesel) at the end of this article for complete circuit.
2. Using a test light connected to 12 volts, probe each of the system ground circuits to ensure a good ground is present. See «PIN VOLTAGE CHARTS - 6.5L DIESEL»(/gmc/suburban/i-1992-1999/remont/pin-voltage-charts/#engine-controls-pin-voltage-charts-65l-diesel) article.

Diagnostic Aids

If engine functions properly, check for a burned out bulb, blown GAUGES or ALT fuse, or an open in the MIL (SERVICE ENGINE SOON) control circuit. This will result in no brake warning light, oil or generator lights, seat belt reminder, etc.

Chart A-1 Flow Chart (6.5L Diesel) No MIL (Service Engine Soon Light - Models W/ PCM). Scheme 115

CHART A-2, NO SCAN DATA, MIL (SERVICE ENGINE SOON) ON AT ALL TIMES OR WILL NOT FLASH MIL (MODELS WITH PCM)

MIL should be on when engine is off and ignition is on. Switched battery voltage is supplied to MIL. The PCM turns light on by providing a ground path through the MIL (SERVICE ENGINE SOON) control circuit. With diagnostic terminal grounded, MIL should flash DTC 12, followed by any other DTC stored in memory. A steady light on indicates a short to ground in the MIL (SERVICE ENGINE SOON) control circuit or an open in the diagnostic request circuit.

Note. Test numbers refer to numbers on diagnostic chart.

1. If there is a problem with PCM that causes scan tester not to read serial data, PCM should not flash DTC 12. If DTC 12 does flash, ensure scan tester is functioning properly (on another vehicle). If scan tester is functioning properly, and serial data circuit is okay, PROM, PCM or SIR DERM may be at fault for the NO DLC symptom.
2. If light goes off when PCM connector is disconnected, MIL (SERVICE ENGINE SOON) control circuit is not shorted to ground.
3. This step checks for an open in the diagnostic request circuit.
4. At this point, MIL wiring is okay. Problem is a faulty PROM. If DTC 12 does not flash, PCM should be replaced using original PROM. Replace PROM only after trying a PCM. A defective PROM usually is an unlikely cause of problem.

Chart A-2 Flow Chart (6.5L Diesel) No Scan Data, MIL (Service Engine Soon) On At All Times Or Will Not Flash MIL (Models With PCM). Scheme 116

CHART A-3, ENGINE CRANKS BUT WILL NOT RUN

This chart assumes battery condition and engine cranking speed are okay, there is adequate fuel in tank, and glow plug system is operating okay.

Note. Test numbers refer to numbers on diagnostic chart.

1. A MIL on is a basic test to determine if there is a 12 volts supply and ignition 12 volts to PCM. No DLC may be due to a PCM problem and CHART A-2 will diagnose PCM.
2. This step will check to see if there is an inject command coming from PCM. NOTE: Use Kent-Moore Digital Volt-Ohmmeter (J 39200) or equivalent.
3. This step will check ground circuit.

If no problem is found in fuel pump circuit or ignition system and cause of a "ENGINE CRANKS BUT WILL NOT RUN" has not been found, check for: water or foreign material in fuel system, and/or a basic engine problem.

Note. If crankshaft position sensor and optical sensor are disconnected or inoperable at the same time this will cause an "ENGINE CRANKS BUT WILL NOT RUN" condition.

Chart A-3 Schematic (6.5L Diesel) Engine Cranks But Will Not Run. Scheme 117

Chart A-3 Flow Chart (6.5L Diesel) Engine Cranks But Will Not Run. Scheme 118

EGR CONTROL PRESSURE/BARO SENSOR OUTPUT CHECK

An EGR control pressure/BARO sensor monitors the amount of vacuum in EGR circuit. It senses actual vacuum in EGR vacuum line and sends a signal back to PCM. The signal is compared to EGR duty cycle calculated by PCM. On vehicles not equipped with EGR, this sensor is only used for a BARO reading.

Note. Test numbers refer to numbers on diagnostic chart.

Note. Use the same diagnostic test equipment for all measurements.

1. Checks sensor output voltage to PCM. This voltage, without engine running, represents a barometer reading to PCM. When comparing scan tester reading to a known good vehicle, it is important to compare vehicles which use a sensor having the same color insert or having the same hot stamped number.
2. Applying 10" Hg (34 kPa) vacuum to sensor should cause voltage to change. Subtract second reading from the first. Voltage difference should be greater than 1.5 volts. When applying vacuum to sensor, change in voltage should be instantaneous. A slow voltage change indicates a faulty sensor.
3. Check vacuum hose to sensor for leaks or restriction. Ensure no other vacuum devices are connected to sensor hose. NOTE: Ensure electrical connector remains securely fastened.
4. To check for intermittent connection, disconnect sensor from bracket and twist sensor by hand. Output changes greater than .1 volt indicates a bad connector or connection. If okay, replace sensor.

EGR Control Press./BARO Sensor Output Check Schematic (6.5L Diesel) EGR Control Pressure/BARO Sensor Output Check. Scheme 119

EGR Control Pressure/BARO Sensor Output Check Flow Chart (6.5L Diesel) EGR Control Pressure/BARO Sensor Output Check. Scheme 120

DTC 13, ENGINE SHUTOFF SOLENOID CIRCUIT FAULT

When ignition switch is in OFF position, engine shutoff solenoid is in NO FUEL position. By providing a ground path, PCM energizes solenoid which then allows fuel to pass into fuel pump. DTC 13 will set when

1. Ignition voltage is present on engine shutoff solenoid control circuit when PCM is requesting engine shutoff solenoid on.

Or

1. No ignition voltage is present on engine shutoff solenoid control circuit when PCM is has requested engine shutoff solenoid off.

PCM will default to a current and history DTC 13 will be stored.

Note. Test numbers refer to numbers on diagnostic chart.

1. Check for open circuit from ignition switch to solenoid.
2. Check engine shutoff solenoid control circuit for open from solenoid to PCM.

An open in either engine shutoff solenoid circuit will cause DTC 13 to set. A no start condition will also exist.

DTC 13 Schematic (6.5L Diesel) Engine Shutoff Solenoid Circuit Fault. Scheme 121

DTC 13 Flow Chart (6.5L Diesel) Engine Shutoff Solenoid Circuit Fault. Scheme 122

DTC 14, ECT SENSOR CIRCUIT LOW (HIGH TEMPERATURE INDICATED)

Engine Coolant Temperature (ECT) sensor is a thermistor that controls signal voltage to PCM. When engine is cold, sensor resistance is high, and PCM will sense a high signal voltage. As engine warms, sensor resistance becomes less and voltage drops. DTC 14 will set when engine coolant temperature is greater than 304°F (151°C) for 2 seconds.

PCM will default to a engine coolant temperature of 171°F (77°C).

Note. Test numbers refer to numbers on diagnostic chart.

1. This step determines if DTC 14 is the result of a hard failure or an intermittent condition.
2. This step determines if ECT signal circuit is shorted to ground.

Check wiring harness routing for a potential short circuit to ground. After starting engine, coolant temperature should rise to about 185°F (85°C). PCM default value will flash on data screen intermittently.

Test engine coolant temperature sensor at various temperature levels to evaluate possibility of a skewed (mis-scaled) sensor. See TEMPERATURE VS RESISTANCE VALUES table. A skewed sensor could result in poor driveability complaints.

DTC 14 Schematic (6.5L Diesel) ECT Sensor Circuit Low (High Temperature Indicated). Scheme 123

DTC 14 Flow Chart (6.5L Diesel) ECT Sensor Circuit Low (High Temperature Indicated). Scheme 124

DTC 15, ECT SENSOR CIRCUIT HIGH (LOW TEMPERATURE INDICATED)

Engine Coolant Temperature (ECT) sensor is a thermistor that controls signal voltage to PCM. When engine is cold, sensor resistance is high, and PCM will sense a high signal voltage. As engine warms, sensor resistance becomes less and voltage drops. DTC 15 will set when engine coolant temperature is less than -33°F (-36°C) and engine has been running for at least 8 minutes.

PCM will default to a engine coolant temperature of 64°F (18°C) and increase idle speed.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step determines if DTC 15 is the result of a hard failure or an intermittent condition.
2. This step determines if ECT signal circuit is open or for a faulty PCM.

Check wiring harness routing for a potential short circuit to ground. After starting engine, coolant temperature should rise to about 185°F (85°C). PCM default value will flash on data screen intermittently.

Test engine coolant temperature sensor at various temperature levels to evaluate possibility of a skewed (mis-scaled) sensor. See TEMPERATURE VS. RESISTANCE VALUES table. A skewed sensor could result in poor driveability complaints.

DTC 15 Flow Chart (6.5L Diesel) ECT Sensor Circuit High (Low Temperature Indicated). Scheme 125

DTC 16, VEHICLE SPEED SIGNAL BUFFER FAULT

Speed sensor circuit consists of a magnetic induction type sensor, a vehicle speed sensor buffer module and wiring. Gear teeth pressed on output shaft induce an alternating current in sensor. This 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.

Transmission output speed signal circuit relays transmission output speed which is used to control shift points, line pressure, TCC, DTC 24 and DTC 72. Vehicle speed signal circuit relays vehicle speed which is used to control engine operating functions and DTC 16. When DTC 24 or 72 is set, 2nd gear only at maximum line pressure will occur. DTC 16 will set when

1. Vehicle speed greater than 20 MPH.
2. 1000-4400 RPM.
3. Vehicle speed signal circuit is open or grounded.
4. All conditions must be met for 2 seconds.

PCM will default to no cruise control or fuel cutoff.

Note. Test numbers refer to numbers on diagnostic chart.

1. This tests for battery voltage at VSS buffer.
2. This tests for proper ground path for vehicle speed sensor signal buffer.
3. This tests for vehicle speed sensor signal buffer signal to PCM.
4. This tests for a signal from VSS buffer to PCM.

Check connections at VSS buffer and PCM. Check for DTC 24 or DTC 72.

DTC 16 Schematic (6.5L Diesel) Vehicle Speed Signal Buffer Fault. Scheme 126

DTC 16 Flow Chart (6.5L Diesel) Vehicle Speed Signal Buffer Fault. Scheme 127

DTC 17, HIGH RESOLUTION CIRCUIT FAULT

Optical sensor provides a high resolution signal to PCM by counting pulses on sensor disk located in injection pump. High resolution signal is one of the most important inputs used by PCM for fuel control and timing. DTC 17 will set when 8 pump cam reference pulses occur without an increase in high resolution counts (internal to PCM). PCM will default to backup fuel.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step determines if a 5-volt reference is present.
2. This step checks ground circuit.
3. This step checks if sensor is sending a signal back to PCM.

When PCM is in backup fuel, fast idle and poor performance problems will exist. If DTC 18 is also stored, a problem with 5-volt reference circuit or sensor ground circuit may exist. If air is present in fuel system, DTC 17 may set.

DTC 17 Schematic (6.5L Diesel) High Resolution Circuit Fault. Scheme 128

DTC 17 Flow Chart (6.5L Diesel) High Resolution Circuit Fault. Scheme 129

DTC 18, PUMP CAM REFERENCE PULSE ERROR

Optical sensor also provides a pump cam signal to PCM by counting pulses on sensor disk located in injection pump. Pump cam reference signal is one of the most important inputs used by PCM for timing and start of injection. DTC 18 will set when 8 cam reference pulses are missed for every crankshaft position pulse. PCM will default to backup fuel.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step determines if DTC 18 is result of a hard failure or an intermittent condition.
2. This step checks 5-volt reference circuits.
3. This step checks ground circuit.
4. This step checks if sensor is sending a signal back to PCM and if an open is present in cam signal circuit.

When PCM is in backup fuel, rough idle and poor performance problems will exist. If DTC 17 is also stored, a problem with 5-volt reference circuit or sensor ground circuit may exist.

DTC 18 Flow Chart (6.5L Diesel) Pump Cam Reference Pulse Error. Scheme 130

DTC 19, CRANKSHAFT POSITION REFERENCE ERROR

Crankshaft position sensor is a Hall Effect type sensor that monitors crankshaft position and speed There are 4 teeth 90 degrees apart on front of crankshaft sprocket that induce an alternating current in sensor which is transmitted to PCM. DTC 19 will set when 8 crankshaft position pulses are missed for every cam reference pulse. PCM will default to backup fuel.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step determines if DTC 19 is result of a hard failure or an intermittent condition.
2. This step checks 5-volt reference circuit.
3. This step checks ground circuit.
4. This step checks sensor and harness wiring.

When PCM is in backup fuel, fast idle and poor performance problems will exist. Check for good connections at crankshaft position sensor and PCM.

DTC 19 Schematic (6.5L Diesel) Crankshaft Position Reference Error. Scheme 131

DTC 19 Flow Chart (6.5L Diesel) Crankshaft Position Reference Error. Scheme 132

DTC 21, APP NO. 1 CIRCUIT HIGH (MODELS WITH PCM)

Accelerator Pedal Position (APP) module provides a voltage signal that changes relative to accelerator position. There are 3 sensors located within APP module that are scaled differently. DTC 21 will set when voltage is greater than 4.75 volts for 2 seconds on APP No. 1 sensor. PCM will default to input from APP No. 1 sensor being ignored. A current and history DTC will set but will not turn on SERVICE THROTTLE SOON light. Throttle will operate normally as long as there is only one sensor malfunctioning.

If 2 different APP sensors have a malfunction, SERVICE THROTTLE SOON light will light and PCM will limit power. If 3 APP sensors malfunction, SERVICE THROTTLE SOON light will light and PCM will only allow engine to operate at idle.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step determines if DTC 21 is result of a hard failure or an intermittent condition.
2. This step checks PCM and wiring.
3. This step checks for an open in ground circuit.

Scan tester displays APP No. 1 position in volts, and should display .45-.95 volt with throttle closed and ignition on or engine at idle. Voltage should increase at a steady rate as throttle is moved toward WOT. Also, 90 percent pedal travel is acceptable for correct APP operation. Monitor APP No. 1 sensor while applying accelerator pedal with engine off and ignition on. Display should vary from about .74 volt with throttle closed, to about 3.7 volts with throttle at WOT. If ground circuit is open or APP signal circuit is shorted to voltage, DTC 21 will set.

DTC 21 Schematic (6.5L Diesel) APP No. 1 Circuit High (Models With PCM). Scheme 133

DTC 21 Flow Chart (6.5L Diesel) APP No. 1 Circuit High (Models With PCM). Scheme 134

DTC 22, APP NO. 1 CIRCUIT LOW (MODELS WITH PCM)

Accelerator Pedal Position (APP) module provides a voltage signal that changes relative to accelerator position. There are 3 sensors located within APP module that are scaled differently. DTC 22 will set when voltage is less than .25 volt for 2 seconds on APP No. 1 sensor.

PCM will default to input from APP No. 1 sensor being ignored. A current and history DTC will set but will not turn on SERVICE THROTTLE SOON light. Throttle will operate normally as long as there is only one sensor malfunctioning. If 2 different APP sensors have a malfunction, SERVICE THROTTLE SOON light will light and PCM will limit power. If 3 APP sensors malfunction, SERVICE THROTTLE SOON light will light and PCM will only allow engine to operate at idle.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step determines if DTC 22 is result of a hard failure or an intermittent condition.
2. This step checks PCM and wiring.
3. This step checks for a faulty connection or sensor.
4. This step checks ground circuit.

Scan tester displays APP No. 1 position in volts, and should display .45-.95 volt with throttle closed and ignition on or engine at idle. Voltage should increase at a steady rate as throttle is moved toward WOT. Also, 90 percent pedal travel is acceptable for correct APP operation.

Monitor APP No. 1 sensor while applying accelerator pedal with engine off and ignition on. Display should vary from about .74 volt with throttle closed, to about 3.7 volts with throttle at WOT. DTC 22 will set if circuit is open.

DTC 22 Flow Chart (6.5L Diesel) APP No. 1 Circuit Low (Models With PCM). Scheme 135

DTC 23, APP NO. 1 CIRCUIT RANGE FAULT

Accelerator Pedal Position (APP) module provides a voltage signal that changes relative to accelerator position. There are 3 sensors located within APP module that are scaled differently. DTC 23 will set when PCM has recognized a skewed (mis-scaled) sensor. PCM compares all 3 sensors to each other and determines if there is a 6 percent difference between APP No. 1 and APP No. 2, and a 10 percent difference to APP No. 3.

PCM will default to input from APP No. 1 sensor being ignored. A current and history DTC will set but will not turn on SERVICE THROTTLE SOON light. Throttle will operate normally as long as there is only one sensor malfunctioning. If 2 different APP sensors have a malfunction, SERVICE THROTTLE SOON light will light and PCM will limit power. If 3 APP sensors malfunction, SERVICE THROTTLE SOON light will light and PCM will only allow engine to operate at idle.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step determines if a good 5-volt reference is present.
2. This step checks for an open in ground circuit.

Scan tester displays APP No. 1 position in volts, and should display .45-.95 volt with throttle closed and ignition on or engine at idle. Voltage should increase at a steady rate as throttle is moved toward WOT. Also, 90 percent pedal travel is acceptable for correct APP operation.

Monitor APP No. 1 sensor while applying accelerator pedal with engine off and ignition on. Display should vary from about .74 volt with throttle closed, to about 3.7 volts with throttle at WOT.

DTC 23 Flow Chart (6.5L Diesel) APP No. 1 Circuit Range Fault. Scheme 136

DTC 24, VSS CIRCUIT LOW (TRANSMISSION OUTPUT SPEED SIGNAL)

Vehicle Speed Sensor (VSS) circuit consists of a magnetic induction type sensor, VSS buffer module, 4WD low switch (if equipped), and wiring. Gear teeth pressed onto output shaft induces an alternating voltage into sensor. This signal is transmitted to VSS buffer module. VSS buffer module compensates for various final drive ratios. VSS buffer module will also convert AC VSS signal into a 40 pulse per revolution DC signal on trans output speed circuit to indicate transmission output speed. On 4WD vehicles, 4WD low signal will also be used for adjustment of 40 pulse per revolution signal to PCM.

DTC 24 will set when

1. Gear selector is not in Park or Neutral.
2. Trans output speed circuit voltage is constant.
3. Engine speed is greater than 3000 RPM.
4. Output speed is less than 250 RPM.
5. MAP is less than 100 kPa.
6. Throttle position is 10-100 percent.
7. All conditions are met for 3 seconds.
8. DTCs 21, 22, 28, 33 or 34 are not set.

PCM will default to 2nd gear only at maximum line pressure.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This test checks for voltage to VSS buffer module.
2. This test checks ground circuit to VSS buffer module.
3. This test checks VSS circuit at VSS buffer module.
4. This test checks for an output speed signal from VSS buffer module.

DTC 24 will set when no vehicle speed is detected at vehicle start off. DTC 72 will set when vehicle speed has been detected and is lost.

DTC 24 Schematic (4L60-E) VSS Circuit Low (Transmission Output Speed Signal). Scheme 137

DTC 24 Schematic (4L80-E) VSS Circuit Low (Transmission Output Speed Signal). Scheme 138

DTC 24 Flow Chart (6.5L Diesel) VSS Circuit Low (Transmission Output Speed Signal). Scheme 139

DTC 25, ACCELERATOR PEDAL POSITION (APP) NO. 2 CIRCUIT HIGH

Accelerator Pedal Position (APP) module provides a voltage signal that changes relative to accelerator position. There are 3 sensors located within APP module that are scaled differently. DTC 25 will set when voltage is greater than 4.75 volts for 2 seconds on APP No. 2 sensor. PCM will default to input from APP No. 2 sensor being ignored. A current and history DTC will set but will not turn on SERVICE THROTTLE SOON light. Throttle will operate normally as long as there is only one sensor malfunctioning.

If 2 different APP sensors have a malfunction, SERVICE THROTTLE SOON light will light and PCM will limit power. If 3 APP sensors malfunction, SERVICE THROTTLE SOON light will light and PCM will only allow engine to operate at idle.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step determines if DTC 25 is result of a hard failure or an intermittent condition.
2. This step checks for an open in ground circuit.
3. This step checks PCM and wiring.

Scan tester displays APP No. 2 position in volts, and should display about 4.5 volts with throttle closed and ignition on or engine at idle. Voltage should decrease at a steady rate as throttle is moved toward WOT. Also, 90 percent pedal travel is acceptable for correct APP operation. Monitor APP No. 2 sensor while applying accelerator pedal with engine off and ignition on. Display should vary from about 4.5 volts with throttle closed, to about 1.5 volts with throttle at WOT.

DTC 25 Flow Chart (6.5L Diesel) Accelerator Pedal Position (APP) No. 2 Circuit High. Scheme 140

DTC 26, ACCELERATOR PEDAL POSITION (APP) NO. 2 CIRCUIT LOW

Accelerator Pedal Position (APP) module provides a voltage signal that changes relative to accelerator position. There are 3 sensors located within APP module that are scaled differently. DTC 26 will set when voltage is less than .25 volt for 2 seconds on APP No. 2 sensor. PCM will default to input from APP No. 2 sensor being ignored. A current and history DTC will set but will not turn on SERVICE THROTTLE SOON light. Throttle will operate normally as long as there is only one sensor malfunctioning.

If 2 different APP sensors have a malfunction, SERVICE THROTTLE SOON light will light and PCM will limit power. If 3 APP sensors malfunction, SERVICE THROTTLE SOON light will light and PCM will only allow engine to operate at idle.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step determines if DTC 26 is result of a hard failure or an intermittent condition.
2. This step checks PCM and wiring.
3. This step checks PCM and sensor signal circuit.

Scan tester displays APP No. 2 position in volts, and should display about 4.5 volts with throttle closed and ignition on or engine at idle. Voltage should decrease at a steady rate as throttle is moved toward WOT. Also, 90 percent pedal travel is acceptable for correct APP operation.

Monitor APP No. 2 sensor while applying accelerator pedal with engine off and ignition on. Display should vary from about 4.5 volts with throttle closed, to about 1.5 volts with throttle at WOT. If 5-volt reference circuit or APP 2 signal circuit is open or shorted to ground, DTC 26 will set.

DTC 26 Flow Chart (6.5L Diesel) Accelerator Pedal Position (APP) No. 2 Circuit Low. Scheme 141

DTC 27, APP NO. 2 CIRCUIT RANGE FAULT

Accelerator Pedal Position (APP) module provides a voltage signal that changes relative to accelerator position. There are 3 sensors located within APP module that are scaled differently. DTC 27 will set when PCM has recognized a skewed (mis-scaled) sensor. PCM compares all 3 sensors to each other and determines if there is a 6 percent difference between APP No. 1 and APP No. 2, and a 10 percent difference to APP No. 3.

PCM will default to input from APP No. 2 sensor being ignored. A current and history DTC will set but will not turn on SERVICE THROTTLE SOON light. Throttle will operate normally as long as there is only one sensor malfunctioning. If 2 different APP sensors have a malfunction, the SERVICE THROTTLE SOON light will light and the PCM will limit power. If 3 APP sensors malfunction, the SERVICE THROTTLE SOON light will light and the PCM will only allow the engine to operate at idle.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step determines if a good 5-volt reference is present.
2. This step checks for an open in ground circuit.

Scan tester displays APP No. 2 position in volts, and should display about 4.5 volts with throttle closed and ignition on or engine at idle. Voltage should decrease at a steady rate as throttle is moved toward WOT. Also, 90 percent pedal travel is acceptable for correct APP operation. Monitor APP No. 2 sensor while applying accelerator pedal with engine off and ignition on. Display should vary from about 4.5 volts with throttle closed, to about 1.5 volts with throttle at WOT.

DTC 27 Flow Chart (6.5L Diesel) APP NO. 2 Circuit Range Fault. Scheme 142

DTC 28, TRANSMISSION RANGE PRESSURE SWITCH CIRCUIT FAULT

Transmission range pressure switch assembly consists of 5 pressure switches (2 normally closed, 3 normally open), and a fluid temperature sensor combined into one unit and mounted on valve body. PCM supplies voltage to each range signal. By grounding one or more of these circuits through various combinations of pressure switches, PCM detects which manual valve position has been selected. With ignition on and engine off, Park/Neutral will be indicated. When transmission electrical connector is disconnected, ground potential for the 3 signals to PCM will be removed, and with ignition on, D2 will be indicated. DTC 28 will set when range signals "A" and "C" are both zero volts (on) for 2 seconds.

PCM will default to harsh shifts, D4 shift control. TCC will be inhibited, and if in hot mode, 4th gear will not be available. DTC 28 will be stored in PCM memory, but will not turn on MIL.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks indicated range signal to manual valve position actually selected.
2. This test checks for correct voltage from PCM to transmission external connector.
3. This test checks for short to ground from PCM to transmission external connector in any one of the 3 circuits.

DTC 28 will set if PCM detects one of 2 illegal combinations. See appropriate TRANSMISSION RANGE PRESSURE SWITCH COMBINATIONS table. Check all wiring connectors for proper terminal tension. For current DTC 28, range signal will default to D4 while A/B/C range values continue to read actual trans. range pressure switch output for each range selection.

TRANSMISSION RANGE PRESSURE SWITCH COMBINATIONS

TRANSMISSION RANGE PRESSURE SWITCH COMBINATIONS (4L60-E) (1)

TRANSMISSION RANGE PRESSURE SWITCH COMBINATIONS (4L80-E) (1)

DTC 28 Schematic (4L60-E) Transmission Range Pressure Switch Circuit Fault. Scheme 143

DTC 28 Schematic (4L80-E) Transmission Range Pressure Switch Circuit Fault. Scheme 144

DTC 28 Flow Chart (6.5L Diesel) Transmission Range Pressure Switch Circuit Fault. Scheme 145

DTC 29, GLOW PLUG RELAY CIRCUIT FAULT

Glow plug system is used to assist 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 plugs by sending a battery voltage signal. PCM will default to hard start. DTC 29 will set when

1. Glow plugs are commanded on and glow plug voltage is less than .8 volt.

Or

1. Glow plugs are off and glow plug voltage is greater than .8 volt.

Or

1. System voltage exceeds glow plug voltage by 2 volts. NOTE: Test numbers refer to numbers on diagnostic chart.

1. This step determines if DTC 29 is result of a hard failure.
2. Scan tester may not display system voltage. It is important that PCM is cycling voltage on and off indicating PCM is okay.
3. This step checks relay feed circuit.
4. This step checks relay ground.
5. This step will determine if an open is present in glow plug relay control circuit.
6. This step checks relay and wiring.

If glow plug relay was stuck in ON position, check for proper operation of glow plugs. When glow plugs are commanded on by scan tester, an internal PCM timer protects glow plug from damage by cycling them on for 3 seconds and then off for 12 seconds.

DTC 29 Schematic (6.5L Diesel) Glow Plug Relay Circuit Fault. Scheme 146

DTC 29 Flow Chart (6.5L Diesel) Glow Plug Relay Circuit Fault. Scheme 147

DTC 31, EGR CONTROL PRESSURE/BARO SENSOR CKT LOW (HIGH VAC)

Manifold Absolute Pressure (MAP) sensor monitors amount of vacuum in EGR circuit and sends a signal back to PCM. Signal is compared to EGR duty cycle calculated by PCM. DTC 31 will set when: actual EGR pressure is less than 15 kPa for 2 seconds. PCM will default to shutting down EGR system.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step determines if DTC 31 is result of a hard failure or an intermittent condition.
2. Attaching a jumper wire between harness terminals "B" (EGR control pressure/BARO signal circuit) to "C" (5-volt reference circuit), will determine if sensor is at fault, or if there is a problem with PCM or wiring.
3. Scan tester may not display 5 volts. It is important that PCM recognized voltage as more than 4 volts, indicating that EGR control pressure/BARO signal circuit and PCM are okay.

With ignition on and engine off, EGR pressure is equal to atmospheric pressure with signal voltage being high. This information is used by PCM as an indication of vehicle altitude. Comparison of this reading with a known good vehicle with the same sensor is a good way to check the accuracy of a suspect sensor. Readings should be the same plus or minus .4 volt. An intermittent open in the EGR control pressure/BARO signal circuit or the 5-volt reference circuit will cause DTC 31 to set.

DTC 31 Flow Chart (6.5L Diesel) EGR Control Pressure/Baro Sensor Circuit Low (High Vacuum). Scheme 148

DTC 32, EGR CIRCUIT ERROR

PCM operates normally-opened solenoid to control EGR valve. By providing a ground path, PCM energizes solenoid allowing vacuum to pass to EGR valve. During normal operation, PCM compares EGR duty cycle signal with EGR control pressure/BARO signal and makes adjustments in duty cycle accordingly. If there is a difference in PCM command and what is sensed by EGR control pressure/BARO sensor, PCM makes minor adjustments to correct. DTC 32 will set when

1. RPM is greater than 506.
2. No DTC 31 or 33 is stored.
3. 50 kPa difference between desired EGR and EGR pressure for 25.5 seconds.

PCM will default to shut down EGR.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step determines if DTC 32 is result of a hard failure or an intermittent condition.
2. This step checks vacuum at EGR vent solenoid.
3. This step checks EGR valve.

A vacuum leak or a pinched vacuum line may cause DTC 32 to set. Check all vacuum hoses and components connected to vacuum hoses for leaks or sharp bends. Check vacuum source to EGR solenoid. Also check for small leak in EGR valve.

DTC 32 Schematic (6.5L Diesel) EGR Circuit Error. Scheme 149

DTC 32 Flow Chart (6.5L Diesel) EGR Circuit Error. Scheme 150

DTC 33, EGR CONTROL PRESSURE/BARO SENSOR CKT HIGH (LOW VAC)

Exhaust Gas Recirculation (EGR) control pressure/BARO sensor monitors amount of vacuum in EGR circuit and sends a signal back to PCM. Signal is compared to EGR duty cycle calculated by PCM.

DTC 33 will set when

1. EGR vent is off.
2. Desired EGR is less than 60 kPa from EGR pressure.
3. EGR pressure is greater than 101 kPa.

PCM will default to shutting down EGR system.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step determines if DTC 33 is result of a hard failure or an intermittent condition.
2. This step simulates conditions for a DTC 31. If PCM recognizes change, PCM, EGR control pressure/BARO signal circuit and 5-volt reference circuit are okay.

With ignition on and engine off, manifold pressure is equal to atmospheric pressure with signal voltage being high. This information is used by PCM as an indication of vehicle altitude. Comparison of this reading with a known good vehicle with the same sensor is a good way to check the accuracy of a suspect sensor. Readings should be the same plus or minus .4 volt.

DTC 33 will set if an open is present in sensor ground circuit, or if EGR control pressure/BARO signal circuit is shorted to voltage or to 5-volt reference circuit. Ensure electrical connectors remain securely fastened. Refer to EGR CONTROL PRESSURE/BARO SENSOR OUTPUT CHECK chart (see link below) for further diagnosis.

1. «EGR CONTROL PRESSURE/BARO SENSOR OUTPUT CHECK»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-tests-wcodes-65l-diesel__egr-control-pressurebaro-sensor-output-check)

DTC 33 Flow Chart (6.5L Diesel) EGR Control Pressure/Baro Sensor Circuit High (Low Vacuum). Scheme 151

DTC 34, INJECTION TIMING STEPPER (ITS) MOTOR CIRCUIT FAULT

PCM controls injection timing with injection timing stepper motor. To increase injection timing PCM extends stepper motor. To retard timing PCM retracts stepper motor. DTC 34 will set when

1. Engine operating at steady RPM.
2. A 5 degree difference exists between measured and desired injection timing for 20.8 seconds. NOTE: Test numbers refer to numbers on diagnostic chart.

1. This step determines if DTC 34 is result of a hard failure or an intermittent condition.
2. This step checks for an open or short in ITS coil 1 low circuit and ITS coil 1 high circuit.
3. This step checks for an open or short in ITS coil 2 low circuit and ITS coil 2 high circuit.
4. The importance of this step is that PCM is sending a varying voltage between 1-12 volts indicating PCM is okay and that problem is with injection timing stepper motor. A steady voltage present on any circuit indicates a problem with PCM or a circuit is shorted to voltage.

A hard start and possible poor performance condition may exist. Measured injection timing will freeze at the point of the fault.

DTC 34 Schematic (6.5L Diesel) Injection Timing Stepper (ITS) Motor Circuit Fault. Scheme 152

DTC 34 Flow Chart (6.5L Diesel) Injection Timing Stepper (ITS) Motor Circuit Fault. Scheme 153

DTC 35, INJECTION PULSE WIDTH ERROR (RESPONSE TIME SHORT)

Fuel injector driver receives an inject command signal from PCM and provides a current regulated output to fuel solenoid that controls injection. It also returns an injection pulse width signal back to PCM to inform it when fuel solenoid has actually seated. This injection pulse width signal is measured in micro seconds. DTC 35 will set when

1. Battery voltage is greater than 10 volts.
2. Engine coolant temperature is greater than 68°F (20°C).
3. Injection pulse width is less than 1.2 milliseconds.

PCM will default to a fixed injection pulse width value of 1.95.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step determines if DTC 35 is result of a hard failure or an intermittent condition.
2. This step checks for an open in fuel inject signal circuit.

Injection pulse width will fluctuate slightly when throttle is depressed.

DTC 35 Schematic (6.5L Diesel) Injection Pulse Width Error (Response Time Short). Scheme 154

DTC 36, INJECTION PULSE WIDTH ERROR (RESPONSE TIME LONG)

Fuel injector driver receives an inject command signal from PCM and provides a current regulated output to fuel solenoid that controls injection. It also returns an injection pulse width signal back to PCM to inform it when the fuel solenoid has actually seated. This injection pulse width signal is measured in micro seconds. DTC 36 will set when

1. Battery voltage is greater than 10 volts.
2. Engine coolant temperature is greater than 68°F (20°C).
3. Injection pulse width is greater than 2.5 milliseconds.

PCM will default to a fixed injection pulse width value of 1.95.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step determines if DTC 36 is result of a hard failure or an intermittent condition.
2. This step determines if solenoid is at fault, or if problem is with PCM or wiring.

Injection pulse width will fluctuate slightly when throttle is depressed. A weak (mechanical failure) fuel solenoid will cause DTC 36 to set.

DTC 36 Schematic (6.5L Diesel) Injection Pulse Width Error (Response Time Long). Scheme 155

DTCS 37/38, TCC BRAKE SWITCH STUCK ON/OFF

Normally closed brake switch supplies a B+ signal on TCC brake switch signal circuit to PCM. When brakes are applied signal voltage is opened.

DTC 37 will set when

1. TCC brake switch signal circuit is open and/or.
2. Vehicle speed is less than 5 MPH for greater than 6 seconds.
3. Then vehicle speed is 5-20 MPH for greater than 6 seconds.
4. Then vehicle speed is greater than 20 MPH for greater than 6 seconds.
5. For a total of 7 times.

DTC 38 will set when

TCC brake switch signal circuit has constant voltage.

* Vehicle speed is greater than 20 MPH for greater than 6 seconds.

* Then vehicle speed is 5-20 MPH for greater than 6 seconds.

* For a total of 7 times.

PCM will default to an incorrect brake signal can affect TCC scheduling. Also, an incorrect brake signal can inhibit 4th gear operation, if in hot mode. DTCS 37/38 will be stored in PCM memory, but will not turn on MIL.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks for voltage at brake switch.
2. This test checks brake switch.
3. This test checks TCC brake switch signal circuit at PCM.

If DTC is intermittent, check customer driving habits and/or for unusual traffic conditions (stop and go, expressway traffic).

DTCS 37/38 Schematic (6.5L Diesel) TCC Brake Switch Stuck On/Off. Scheme 156

DTCS 37/38 Flow Chart (6.5L Diesel) TCC Brake Switch Stuck On/Off. Scheme 157

DTC 39, TCC STUCK OFF (4L80-E)

PCM commands TCC PWM solenoid on by modulating TCC signal fluid acting on the converter clutch shift valve. Then TCC apply fluid applies the torque converter clutch.

DTC 39 will set when

1. DTCs 28, 71 or 74 are not set.
2. TCC is commanded on.
3. TCC slip speed greater than 65 RPM.
4. Trans. range in D3 or D4.
5. 2nd or 3rd gear.
6. All conditions are met for 2 seconds.

PCM will default to no 4th gear in hot mode.

Note. Test numbers refer to numbers on diagnostic chart.

1. This checks mechanical and hydraulic operation of TCC, while commanded on by PCM.

Snapshot mode will record 5 data parameters per second.

DTC 39 Schematic (4L80-E) TCC Stuck Off. Scheme 158

DTC 39 Flow Chart (4L80-E) TCC Stuck Off. Scheme 159

DTC 41, BRAKE SWITCH CIRCUIT FAULT

TCC normally closed brake switch supplies a battery voltage signal on TCC brake switch signal circuit to PCM. Circuit is open when brakes are applied. Brake light/cruise control normally open brake switch supplies a battery voltage signal on cruise control/brake switch signal circuit to PCM when brakes are applied. DTC 41 will set when

1. Switches disagree for 10 consecutive minutes.

Or

1. TCC and cruise control brake switches are not toggling open and closed during 6 brake applications on same ignition cycle.

PCM will default to an incorrect brake signal can affect TCC, 4th gear operation, in hot mode and cruise control.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step checks for voltage at brake switch.
2. This step simulates brake switch closed or brakes off.
3. This step checks for ignition feed to TCC brake switch.
4. This step checks TCC brake switch signal circuit and simulates brakes being applied.

Check customer driving habits and/or unusual traffic conditions (i.e. stop and go expressway traffic).

DTC 41 Schematic (6.5L Diesel) Brake Switch Circuit Fault. Scheme 160

DTC 41 Flow Chart (6.5L Diesel) Brake Switch Circuit Fault. Scheme 161

DTC 42, FUEL TEMP CIRCUIT LOW (HIGH TEMP INDICATED)

Fuel temperature sensor is a thermistor that controls signal voltage to PCM. When fuel is cold, sensor resistance is high, and PCM will sense a high signal voltage. As fuel warms, sensor resistance becomes less and voltage drops. Fuel temperature sensor is integrated with optical sensor. DTC 42 will set when fuel temperature is greater than 215°F (102°C) for 2 seconds. PCM will default to poor idle quality during hot conditions.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step determines if DTC 42 is result of a hard failure or an intermittent condition.
2. This step determines if fuel temperature signal circuit is shorted to ground.

Scan tester reads fuel temperature in degrees centigrade. After engine is running, temperature should rise steadily. DTC 42 will set if a connection is faulty, or an open is present in fuel temperature signal circuit or sensor ground circuit. Test fuel temperature sensor at various temperature levels to evaluate possibility of a skewed (mis-scaled) sensor. See TEMPERATURE VS. RESISTANCE VALUES table.

DTC 42 Flow Chart (6.5L Diesel) Fuel Temperature Circuit Low (High Temperature Indicated). Scheme 162

DTC 43, FUEL TEMP CIRCUIT HIGH (LOW TEMP INDICATED)

Fuel temperature sensor is a thermistor that controls signal voltage to PCM. When fuel is cold, sensor resistance is high, and PCM will sense a high signal voltage. As fuel warms, sensor resistance becomes less and voltage drops. Fuel temperature sensor is integrated with optical sensor.

DTC 43 will set when fuel temperature is less than 6°F (-14°C) and engine has been running for at least 2 minutes. PCM will default to poor idle quality during hot conditions.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step determines if DTC 43 is result of a hard failure or an intermittent condition.
2. This step simulates a DTC 42. If PCM recognizes low signal voltage (high temperature), PCM and wiring are okay.
3. This step determines if an open is present in fuel temperature signal circuit. 5 volts should exist at sensor connector. This will determine if a wiring problem exists or if PCM is faulty.

Scan tester reads fuel temperature in degrees centigrade. After engine is running, temperature should rise steadily. DTC 43 will set if a connection is faulty, or an open is present in fuel temperature signal circuit or sensor ground circuit. Test fuel temperature sensor at various temperature levels to evaluate possibility of a skewed (mis-scaled) sensor. See TEMPERATURE VS. RESISTANCE VALUES table.

DTC 43 Flow Chart (6.5L Diesel) Fuel Temperature Circuit High (Low Temperature Indicated). Scheme 163

DTC 44, EGR PULSE WIDTH ERROR

PCM operates the normally-open solenoid to control EGR valve. By providing a ground path, PCM energizes solenoid allowing vacuum to pass to EGR. During normal operation, PCM compares EGR duty cycle signal with EGR control pressure/BARO signal and makes adjustments in duty cycle accordingly. If there is a difference in PCM command and what is at EGR valve sensed by EGR control pressure/BARO sensor, PCM makes minor adjustments to correct. DTC 44 will set when

1. Ignition voltage is present on the EGR control circuit when EGR solenoid is commanded on.

Or

1. No ignition voltage is present on EGR control circuit when EGR solenoid is commanded off.

PCM will default to shut down EGR.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step determines if DTC 44 is result of a hard failure or an intermittent condition.
2. This step checks if PCM and wiring are okay.
3. This step checks voltage at EGR solenoid.

An open in ignition feed circuit or the EGR control circuit will cause DTC 44 to set.

DTC 44 Schematic (6.5L Diesel) EGR Pulse Width Error. Scheme 164

DTC 44 Flow Chart (6.5L Diesel) EGR Pulse Width Error. Scheme 165

DTC 45, EGR VENT ERROR

When PCM recognizes operating range for no EGR, PCM energizes EGR vent solenoid which allows rapid venting of EGR vacuum. This solenoid is normally open. DTC 45 will set when

1. Ignition voltage is present on EGR vent control circuit when EGR vent is commanded on.

Or

1. No ignition voltage is present on EGR vent control circuit when EGR vent is commanded off.

PCM will default to shut off EGR system.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step determines if DTC 45 is result of a hard failure or an intermittent condition.
2. This step checks if PCM and wiring are okay.
3. This step checks power and control circuits.

An open in ignition feed circuit or EGR vent control circuit will cause DTC 45 to set.

DTC 45 Flow Chart (6.5L Diesel) EGR Vent Error. Scheme 166

DTC 46, MALFUNCTION INDICATOR LIGHT (MIL) CIRCUIT FAULT

MIL should always light when ignition is on and engine is not running for 2 seconds. PCM controls MIL by providing a ground path. DTC 46 will set when

1. Ignition voltage on MIL control circuit when PCM is requesting MIL on.

Or

1. No ignition voltage on MIL control circuit when PCM is requesting MIL off.

PCM will default to no MIL.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step checks PCM's ability to command MIL.
2. This step determines if an open is present in ignition feed circuit or MIL control circuit.

Check for a faulty bulb or fuse. An open in MIL control circuit will cause DTC 46 to set.

DTC 46 Schematic (6.5L Diesel) Malfunction Indicator Light (MIL) Circuit Fault. Scheme 167

DTC 46 Flow Chart (6.5L Diesel) Malfunction Indicator Light (MIL) Circuit Fault. Scheme 168

DTC 47, IAT SENSOR CIRCUIT LOW (HIGH TEMPERATURE INDICATED)

Intake Air Temperature (IAT) sensor is a thermistor that controls signal voltage to PCM. When air is cold, sensor resistance is high, and PCM will sense a high signal voltage. As air warms, sensor resistance becomes less and voltage drops. DTC 47 will set when

1. Engine coolant temperature is less than 100°F (38°C).
2. Intake air temperature is greater than 205°F (96°C) for 2 seconds.

PCM will default to poor engine performance during cold operation.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step determines if DTC 47 is result of a hard failure or an intermittent condition.
2. This step determines if IAT signal circuit is shorted to ground.

Check wiring harness routing for a potential short circuit to ground in IAT signal circuit. Scan tester displays intake air temperature in degrees centigrade. A faulty connection or an open in IAT signal circuit or sensor ground circuit will cause DTC 47 to set. Test intake air temperature sensor at various temperature levels to evaluate the possibility of a skewed (mis-scaled) sensor. See TEMPERATURE VS. RESISTANCE VALUES table. A skewed sensor could result in poor driveability complaints.

DTC 47 Flow Chart (6.5L Diesel) IAT Sensor Circuit Low (High Temperature Indicated). Scheme 169

DTC 48, IAT SENSOR CIRCUIT HIGH (LOW TEMPERATURE INDICATED)

Intake Air Temperature (IAT) sensor is a thermistor that controls signal voltage to PCM. When air is cold, sensor resistance is high, and PCM will sense a high signal voltage. As air warms, sensor resistance becomes less and voltage drops. DTC 48 will set when intake air temperature is less than -39°F (-38°C) for 2 minutes. PCM will default to poor engine performance during cold operation.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step determines if DTC 48 is result of a hard failure or an intermittent condition.
2. This step determines if IAT signal circuit is shorted to ground.
3. This step determines if a wiring problem is present or if PCM is faulty.

Check wiring harness routing for a potential short circuit to ground in IAT signal circuit. Scan tester displays intake air temperature in degrees centigrade. A faulty connection or an open in IAT signal circuit or sensor ground circuit will cause DTC 48 to set. Test intake air temperature sensor at various temperature levels to evaluate possibility of a skewed (mis-scaled) sensor. See TEMPERATURE VS. RESISTANCE VALUES table. A skewed sensor could result in poor driveability complaints.

DTC 48 Flow Chart (6.5L Diesel) IAT Sensor Circuit High (Low Temperature Indicated). Scheme 170

DTC 49, SERVICE THROTTLE SOON LIGHT CIRCUIT FAULT

SERVICE THROTTLE SOON light should always light when ignition is on and engine is not running for 2 seconds. PCM controls SERVICE THROTTLE SOON light by providing a ground path. DTC 49 will set when

1. Ignition voltage on SERVICE THROTTLE SOON light control circuit when PCM is requesting SERVICE THROTTLE SOON light on.

Or

1. No ignition voltage on SERVICE THROTTLE SOON light control circuit when PCM is requesting SERVICE THROTTLE SOON light off.

PCM will default to MIL will not light, but a current and history DTC 49 will set.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step checks PCM's ability to command SERVICE THROTTLE SOON light.
2. This step determines if an open is present in ignition feed circuit or SERVICE THROTTLE SOON light control circuit.

Check for a faulty bulb or fuse. An open in SERVICE THROTTLE SOON light control circuit will cause DTC 49 to set.

DTC 49 Flow Chart (6.5L Diesel) Service Throttle Soon Light Circuit Fault. Scheme 171

DTC 51, PROM PROBLEM (FAULTY OR INCORRECT PROM)

Ensure all pins are fully inserted in socket. If pins are fully inserted, replace PROM, clear memory and recheck. If DTC 51 resets, replace PCM. If PCM is faulty and must be replaced, TDC OFFSET must be programmed into new PCM. When all diagnosis and repairs are complete, clear DTCS and verify for proper operation.

DTCS 52/53, SYSTEM VOLTAGE HIGH LONG

Battery voltage input circuit is battery feed for PCM. Ignition voltage input circuit is ignition feed for PCM. DTC 52 will set when ignition is on and PCM battery voltage input circuit terminal voltage is greater than 16 volts for 109 minutes. DTC 53 will set when ignition is on and PCM battery voltage input circuit terminal voltage is greater than 19.5 volts for 2 seconds. PCM will default to the pressure control solenoid is turned off, 3-2 control solenoid is turned off, transmission shifts immediately to 3rd gear, and TCC operation will be inhibited. The setting of additional DTCS may result.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks that normal battery voltage is 9-15 volts.
2. This test checks if generator is faulty under load conditions.

Battery voltage input circuit supplies battery voltage to PCM. Charging battery with a battery charger and jump-starting an engine may set DTCS 52/53. If DTC sets when an accessory is operated, check for faulty connections or excessive current draw. Check for faulty connections at starter solenoid or fusible link.

DTCS 52/53 Schematic (6.5L Diesel) System Voltage High Long. Scheme 172

DTCS 52/53 Flow Chart (6.5L Diesel) System Voltage High Long. Scheme 173

DTC 54, PCM FUEL CIRCUIT ERROR

This DTC indicates a fault in fueling circuit of PCM is present. Check if DTC 17 is also stored. If DTC 17 is set, refer to DTC 17 chart first. If DTC 17 is not set, replace PCM. If PCM is faulty and must be replaced, TDC OFFSET must be programmed into new PCM. When all diagnosis and repairs are complete, clear DTCS and verify for proper operation.

DTC 56, INJECTION PUMP CALIBRATION RESISTOR ERROR

PCM uses a calibrated resistor mounted internally in injection pump to determine fuel rates. Resistor value is stored in PCM memory. If PCM memory has been disturbed or PCM has been replaced, PCM will relearn resistor value on next ignition cycle. DTC 56 will set when PCM has lost its memory and is unable to read a resistor value on the next ignition cycle. Possible poor performance problem. PCM will light MIL and a current and history DTC 56 will set. PCM will default to the lowest fuel table.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step determines if a problem exists with fuel solenoid driver connection or if injection pump is faulty.

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

DTC 56 Flow Chart (6.5L Diesel) Injection Pump Calibration Resistor Error. Scheme 174

DTC 57, PCM 5-VOLT SHORTED

The 5-volt reference is a non-varying calculated voltage. DTC 57 will set when 5-volt reference is less than one volt. PCM will default to backup fuel, no EGR and no turbo boost.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step confirms that a DTC is still present.
2. This step checks that a 5-volt reference is present from PCM.
3. This step determines if a short to ground is present in 5-volt reference circuits or in PCM.

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

DTC 57 Schematic (6.5L Diesel) PCM 5-Volt Shorted. Scheme 175

DTC 57 Flow Chart (6.5L Diesel) PCM 5-Volt Shorted. Scheme 176

DTC 58, TRANSMISSION FLUID TEMP SENSOR CIRCUIT LOW (HIGH TEMP INDICATED) - 4L60-E & 4L80-E

Transmission Fluid Temperature (TFT) sensor is a thermistor within transmission range pressure switch assembly, that controls signal voltage to PCM. PCM applies voltage on 5V TFT signal circuit to sensor. When transmission fluid is cold, sensor resistance is high and PCM will sense high signal voltage.

As transmission fluid temperature warms to normal transmission operating temperature of 212°F (100°C), sensor resistance becomes less and voltage decreases to 1.5-2.0 volts. If DTC 79 is also set, check transmission cooling system. DTC 58 will set when signal voltage indicates TFT greater than 306°F (151°C) for one second.

PCM will default to when DTC 58 is set, transmission will use a warm value for operation, but scan tester will display actual fluid temperature. TCC solenoid will be on in 3rd and 4th gears. Shifts will occur early. DTC 58 will be stored in PCM memory but will not turn on MIL.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks for a short to ground or a skewed sensor.
2. This test checks for an internal fault within transmission by creating an open.

Check harness routing for a potential short to ground in 5V TFT signal circuit. Scan tester TFT display should rise steadily to about 212°F (100°C) then stabilize. Test transmission fluid temperature sensor at various temperature levels to evaluate the possibility of a skewed (mis-scaled) sensor. See TEMPERATURE VS. RESISTANCE VALUES table. A skewed sensor could result in delayed garage shifts or TCC complaints.

TEMPERATURE VS. RESISTANCE VALUES (1) (2)

DTC 58 Schematic (4L80-E) Transmission Fluid Temp. Sensor Circuit Low (High Temp. Indicated). Scheme 177

DTC 58 Flow Chart (All Models) Transmission Fluid Temp. Sensor Circuit Low (High Temp. Indicated). Scheme 178

DTC 59, TRANSMISSION FLUID TEMP SENSOR CIRCUIT HIGH (LOW TEMP INDICATED) - 4L60-E & 4L80-E

Transmission Fluid Temperature (TFT) sensor is a thermistor within transmission range pressure switch assembly that controls signal voltage to the PCM. PCM applies voltage on 5-volt TFT signal circuit to sensor. When transmission fluid is cold, sensor resistance is high and PCM will sense high signal voltage.

As transmission fluid temperature warms to normal transmission operating temperature of 212°F (100°C), sensor resistance becomes less and voltage decreases to 1.5-2.0 volts. DTC 59 will set when signal voltage indicates TFT less than 40°F (40°C) for one second.

PCM will default to when DTC 59 is set, transmission will use a warm value for operation, but scan tester will display actual fluid temperature. TCC may not apply properly. DTC 59 will be stored in PCM memory but will not turn on MIL.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks for a skewed sensor.
2. This test simulates a DTC 58. If PCM recognizes low signal voltage (high temperature), and scan tester displays 295°F (146°C) or greater, PCM and wiring are okay.
3. This test checks if 5-volt TFT signal circuit is open. Five volts should be present at sensor connector when measure using DVOM.

Scan tester displays transmission fluid temperature in degrees. After transmission is operating, temperature should rise steadily to about 212°F (100°C) then stabilize. A faulty connection or open in sensor ground circuit or 5-volt TFT signal circuit may cause DTC 59 to set.

Test transmission fluid temperature sensor at various temperature levels to evaluate possibility of a skewed (mis-scaled) sensor. See TEMPERATURE VS. RESISTANCE VALUES table. A skewed sensor could result in firm shifts or TCC complaints.

TEMPERATURE VS. RESISTANCE VALUES (1) (2)

DTC 59 Flow Chart (All Models) Transmission Fluid Temp. Sensor Circuit High (Low Temp. Indicated). Scheme 179

DTC 61, TURBO BOOST SENSOR CIRCUIT HIGH

PCM sends a 5-volt reference signal to boost sensor. As manifold pressure changes, electrical resistance of boost sensor also changes. By monitoring sensor output voltage, PCM detects how much pressure is being produced by turbocharger in intake manifold. PCM uses boost sensor to control turbo boost and fuel at different loads. DTC 61 will set when

1. Boost signal voltage is greater than 3.9 volts.
2. RPM is less than 3500. PCM will default to no turbo boost and poor performance. NOTE: Test numbers refer to numbers on diagnostic chart.

1. This step determines if DTC 61 is result of a hard failure or an intermittent condition.
2. This step simulates conditions for DTC 62. If PCM recognizes change, then PCM and boost signal circuit are okay.
3. This step checks for an open in ground circuit.

With ignition on and engine not running, boost pressure is equal to atmospheric pressure with signal voltage being high. Comparison of this reading with a known good vehicle using the same sensor is a good way to check accuracy of a suspect sensor. Readings should be the same plus or minus .4 volt. Very little boost can be attained by revving the engine in Neutral.

DTC 61 Flow Chart (6.5L Diesel) Turbo Boost Sensor Circuit High. Scheme 180

DTC 62, TURBO BOOST SENSOR CIRCUIT LOW

PCM sends a 5-volt reference signal to boost sensor. As manifold pressure changes, electrical resistance of boost sensor also changes. By monitoring sensor output voltage, PCM detects how much pressure is being produced by turbocharger in intake manifold. PCM uses boost sensor to control turbo boost and fuel at different loads. DTC 62 will set when boost signal voltage is less than .8 volt. PCM will default to no turbo boost and limited fuel.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step determines if DTC 62 is result of a hard failure or an intermittent condition.
2. This step simulates conditions for DTC 61. If PCM recognizes change, then PCM, 5-volt reference circuit and boost signal circuit are okay.

With ignition on and engine not running, boost pressure is equal to atmospheric pressure with signal voltage being high. Comparison of this reading with a known good vehicle using the same type sensor is a good way to check accuracy of a suspect sensor. Readings should be the same plus or minus .4 volt. Very little boost can be attained by revving the engine in Neutral.

DTC 62 Flow Chart (6.5L Diesel) Turbo Boost Sensor Circuit Low. Scheme 181

DTC 63, APP NO. 3 CIRCUIT HIGH (MODELS WITH PCM)

Accelerator Pedal Position (APP) module provides a voltage signal that changes relative to accelerator position. There are 3 sensors located within APP module that are scaled differently. DTC 63 will set when voltage is greater than 4.75 volts for 2 seconds on APP No. 3 sensor.

PCM will default to input from APP No. 3 sensor being ignored. A current and history DTC will set but will not turn on SERVICE THROTTLE SOON light. Throttle will operate normally as long as there is only one sensor malfunctioning. If 2 different APP sensors have a malfunction, SERVICE THROTTLE SOON light will light and PCM will limit power. If 3 APP sensors malfunction, SERVICE THROTTLE SOON light will light and PCM will only allow engine to operate at idle.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step determines if DTC 63 is result of a hard failure or an intermittent condition.
2. This step checks PCM and wiring.
3. This step checks for an open in ground circuit and PCM.

Scan tester displays APP No. 3 position in volts, and should display 4 volts with throttle closed and ignition on or engine at idle. Voltage should decrease at a steady rate as throttle is moved toward WOT. Also, 90 percent pedal travel is acceptable for correct APP operation.

Monitor APP No. 3 sensor while applying accelerator pedal with engine off and ignition on. Display should vary from about 4 volts with throttle closed, to about 2 volts with throttle at WOT.

DTC 63 Flow Chart (6.5L Diesel) Accelerator Pedal Position (APP) No. 3 Circuit High (Models With PCM). Scheme 182

DTC 64, APP NO. 3 CIRCUIT LOW (MODELS WITH PCM)

Accelerator Pedal Position (APP) module provides a voltage signal that changes relative to accelerator position. There are 3 sensors located within APP module that are scaled differently. DTC 64 will set when voltage is less than .25 volt for 2 seconds on APP No. 3 sensor.

PCM will default to input from APP No. 3 sensor being ignored. A current and history DTC will set but will not turn on SERVICE THROTTLE SOON light. Throttle will operate normally as long as there is only one sensor malfunctioning. If 2 different APP sensors have a malfunction, SERVICE THROTTLE SOON light will light and PCM will limit power. If 3 APP sensors malfunction, SERVICE THROTTLE SOON light will light and PCM will only allow engine to operate at idle.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step determines if DTC 64 is result of a hard failure or an intermittent condition.
2. This step checks PCM and wiring.
3. This step checks PCM and sensor signal circuit.

Scan tester displays APP No. 3 position in volts, and should display 4 volts with throttle closed and ignition on or engine at idle. Voltage should decrease at a steady rate as throttle is moved toward WOT. Also, 90 percent pedal travel is acceptable for correct APP operation.

Monitor APP No. 3 sensor while applying accelerator pedal with engine off and ignition on. Display should vary from about 4 volts with throttle closed, to about 2 volts with throttle at WOT. If the 5-volt reference circuit is open or the APP 3 signal circuit is shorted to ground, DTC 64 will set.

DTC 64 Flow Chart (6.5L Diesel) APP NO. 3 Circuit Low (Models With PCM). Scheme 183

DTC 65, APP NO. 3 CIRCUIT RANGE FAULT

Accelerator Pedal Position (APP) module provides a voltage signal that changes relative to accelerator position. There are 3 sensors located within APP module that are scaled differently. DTC 65 will set when PCM has recognized a skewed (mis-scaled) sensor. PCM compares all 3 sensors to each other and determines if there is a 6 percent difference between APP No. 1 and APP No. 2, and a 10 percent difference to APP No. 3.

PCM will ignore input from APP No. 3. A current and history DTC will set but will not turn on SERVICE THROTTLE SOON light. Throttle will operate normally as long as there is only one sensor malfunctioning. If 2 different APP sensors have a malfunction, SERVICE THROTTLE SOON light will light and PCM will limit power. If 3 APP sensors malfunction, SERVICE THROTTLE SOON light will light and PCM will only allow engine to operate at idle.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step determines if a good 5-volt reference is present.
2. This step checks for an open in ground circuit.

Scan tester displays APP No. 3 position in volts, and should display 4 volts with throttle closed and ignition on or engine at idle. Voltage should decrease at a steady rate as throttle is moved toward WOT. Also, 90 percent pedal travel is acceptable for correct APP operation.

Monitor APP No. 3 sensor while applying accelerator pedal with engine off and ignition on. Display should vary from about 4 volts with throttle closed, to about 2 volts with throttle at WOT.

DTC 66, 3-2 CONTROL SOLENOID CIRCUIT FAULT (4L60-E)

Hydraulically, the 3-2 control solenoid coordinates apply rate of 2-4 band with hydraulic release, of 3-4 clutch during a 3-2 downshift. PCM continually monitors 3-2 circuit duty cycle depending on commanded state of circuit. When transmission is in 1st gear, duty cycle of solenoid is equal to zero. When transmission is in 2nd gear or higher, duty cycle of solenoid will be about 90 percent. When transmission downshifts, 3-2, duty cycle of solenoid will drop. DTC 66 will set when

1. PCM commands solenoid on and voltage remains high (B+) for 4 seconds.
2. PCM commands solenoid off and voltage remains low (zero volts) for 4 seconds.

PCM will default to a delayed (soft) landing to 3rd gear and 3rd gear starts.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks function of 3-2 control solenoid and internal transmission harness.
2. This test checks for power to 3-2 control solenoid from ignition through fuse.

Check all connections at transmission connector. 3-2 control solenoid feedback normally oscillate on/off when duty cycle is applied. An open in ignition feed circuit will cause multiple DTCS to set.

DTC 66 Schematic (4L60-E) 3-2 Control Solenoid Circuit Fault. Scheme 184

DTC 66 Flow Chart (4L60-E) 3-2 Control Solenoid Circuit Fault. Scheme 185

DTC 67, TCC SOLENOID CIRCUIT FAULT (4L60-E)

Ignition voltage is supplied directly to TCC solenoid. PCM controls solenoid by providing ground path through TCC control circuit. DTC 67 will set when

1. PCM commands solenoid on and voltage remains high (B+) for 2 seconds.
2. PCM commands solenoid off and voltage remains low (zero volts) for 2 seconds.

PCM will default to no TCC and no 4th gear in hot mode.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks PCM's ability to control solenoid.
2. This test checks power supply to TCC solenoid.

Check all connections at transmission connector. Some slight TCC slip is normal. An open in ignition feed circuit will cause multiple DTCS to set. A short to ground in TCC circuit may also cause DTC 69 to set. If TCC circuit is shorted to ground, TCC will hydraulically engage in D2.

DTC 67 Schematic (4L60-E) TCC Solenoid Circuit Fault. Scheme 186

DTC 67 Flow Chart (4L60-E) TCC Solenoid Circuit Fault. Scheme 187

DTC 68, TRANSMISSION COMPONENT SLIPPING (4L80-E)

PCM monitors difference in engine speed and input speed. With transmission in Drive and TCC locked, scan tester should display engine speed closely matching input speed. DTC 68 will set when

1. DTCs 28, 71 or 74 are not set.
2. TCC slip speed greater than 200 RPM.
3. 4th gear is indicated.
4. TCC is locked.
5. Not in Park/Neutral.
6. All conditions are met for 2 seconds.

PCM will default to inhibit TCC operation.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks the indicated range signal to actual selected range. A faulty switch could set DTC 68.
2. This test checks torque converter for slippage while in commanded lock-up state.

Check for deformed connectors at pass-thru connector. DTC 68 will set when going to default (2nd gear). An intermittent incorrect engine speed signal will set a DTC 68 if incorrect signal lasts for greater than 2 seconds. A mechanical failure in 1-2 shift solenoid (stuck off) or 2-3 shift solenoid (stuck on) could set DTC 68.

DTC 68 Flow Chart (4L80-E) Transmission Component Slipping. Scheme 188

DTC 69, TCC STUCK ON (4L60-E)

PCM energizes TCC solenoid by grounding TCC control circuit with an internal quad-driver. When grounded (energized) by PCM, TCC solenoid stops converter signal oil from exhausting. TCC solenoid will de-energize when quad-driver no longer provides a ground. When TCC solenoid is de-energized, it will block exhaust fluid and release TCC. DTC 69 will set when

1. DTCs 21, 22 or 28 are not set.
2. TCC slip speed indicates -20-20 RPM.
3. TCC solenoid is commanded off.
4. TP sensor signal is greater than 25 percent.
5. Trans. range switch indicates D3 or D4.
6. Commanded gear indicates 3rd or 4th gear.
7. Engine speed is greater than 300 RPM.
8. All conditions are met for 4 seconds.

PCM will default to early shift pattern.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks mechanical state of TCC. When PCM commands TCC solenoid off, TCC slip speed should increase.

If TCC is mechanically stuck on, vehicle speed is zero, brakes are applied and D2 is selected, TCC fluid will mechanically apply TCC causing an engine stall.

DTC 69 Schematic (4L60-E) TCC Stuck On. Scheme 189

DTC 69 Flow Chart (4L60-E) TCC Stuck On. Scheme 190

DTC 69, TCC STUCK ON (4L80-E)

PCM commands TCC PWM solenoid on by modulating TCC signal fluid acting on converter clutch shift valve. Then TCC apply fluid applies torque converter clutch. DTC 69 will set when

1. DTCs 21, 22, 28, 71 or 74 are not set.
2. TCC slip speed indicates -5-10 RPM.
3. TCC solenoid is commanded off.
4. TP sensor signal is greater than 25 percent.
5. Trans. range switch indicates D3 or D4.
6. Commanded gear indicates 2nd or 3rd gear.
7. All conditions are met for 2 seconds. NOTE: Test numbers refer to numbers on diagnostic chart.

1. This test checks for proper throttle position sensor operation.
2. This test checks mechanical state of TCC. When PCM commands TCC solenoid off, TCC slip should increase.

If TCC is mechanically stuck on, vehicle speed is zero, brakes are applied and D2 is selected, TCC fluid will mechanically apply TCC causing an engine stall.

Scan TP signal while depressing accelerator pedal with engine off and ignition on. Display should vary from less than .85 volt when throttle is closed to greater than 4 volts when throttle is held at WOT. Incorrect TP sensor values may affect TCC operation.

DTC 69 Flow Chart (4L80-E) TCC Stuck On. Scheme 191

DTC 71, SET/COAST SWITCH FAULT (MODELS WITH PCM)

Cruise ON/OFF, SET/COAST and RESUME/ACCEL switches are inputs to fuel control portion of PCM. These inputs allow PCM to control and hold a requested speed. Set/coast request signal circuit supplies ignition voltage to PCM when set/coast is depressed. DTC 71 will set when

1. Cruise control is on.
2. Ignition voltage on set/coast request signal circuit is present for more than 25.5 seconds.

PCM will default to disallowing all cruise inputs. TCC shift schedules may be affected.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step determines if cruise control switch is okay.
2. This step determines if PCM or switch is at fault.

Check for SET/COAST switch stuck in the engage position or for a short to voltage in the set/coast request signal circuit.

DTC 71 Schematic (6.5L Diesel) Set/Coast Switch Fault (Models With PCM). Scheme 192

DTC 71 Flow Chart (6.5L Diesel) Set/Coast Switch Fault (Models With PCM). Scheme 193

DTC 72, SPEED SENSOR CIRCUIT LOSS (TRANS OUTPUT SPEED SIGNAL) - 4L60-E & 4L80-E

Vehicle Speed Sensor (VSS) circuit consists of a magnetic induction type sensor, VSS buffer module, 4WD low switch (if equipped) and wiring. Gear teeth pressed onto output shaft induces an alternating voltage into sensor. This signal is transmitted to VSS buffer module. VSS buffer module compensates for various final drive ratios. VSS buffer module will also convert AC VSS signal into a 40 pulse per revolution DC signal on trans. output speed circuit to indicate transmission output speed. On 4WD vehicles, 4WD low signal will also be used for adjustment of the 40 pulse per revolution signal to PCM.

DTC 72 will set when

Gear selector is not in Park or Neutral.

1. Transmission output speed change is greater than 1000 RPM.
2. Engine speed is greater than 200 RPM.
3. All conditions are met for 2 seconds.
4. DTC 28 is not set.

Or

Gear selector is in Park or Neutral.

1. Transmission output speed change is greater than 2050 RPM.
2. Engine speed is greater than 200 RPM.
3. All conditions are met for 2 seconds.
4. DTC 28 is not set.

PCM will default to a soft (delayed) landing to 2nd gear and 2nd gear starts.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This test checks for voltage to VSS buffer module.
2. This test checks ground circuit to VSS buffer module.
3. This test checks VSS circuit at VSS buffer module.
4. This test checks for an output speed signal from VSS buffer module.

DTC 24 will set when no vehicle speed is detected at vehicle start off. DTC 72 will set when vehicle speed has been detected and is lost.

DTC 72 Flow Chart (All Models) Speed Sensor Circuit Loss (Transmission Output Speed Signal). Scheme 194

DTC 73, PRESSURE CONTROL SOLENOID CIRCUIT (CURRENT ERROR)

Pressure control solenoid is a PCM-controlled device used to regulate transmission line pressure. PCM compares TP voltage, engine RPM and other inputs to determine line pressure appropriate for a given load. PCM will regulate pressure by applying a varying amperage to pressure control solenoid. The applied amperage can vary from .1-1.1 amp. PCM then monitors amperage at the return line. DTC 73 will set when return amperage varies greater than .16 amp from commanded amperage for at least one second and DTC 75 is not set.

PCM will default to full line pressure being applied, causing harsh shifts. DTC 73 will be stored in PCM memory but will not turn on MIL.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This test checks PCM's ability to command pressure control solenoid.
2. This test checks internal transmission harness and pressure control solenoid for correct resistance.

Check for poor connections at PCM and transmission connector.

DTC 73 Schematic (6.5L Diesel) Pressure Control Solenoid Circuit (Current Error). Scheme 195

DTC 73 Flow Chart (6.5L Diesel) Pressure Control Solenoid Circuit (Current Error). Scheme 196

DTC 74, TRANSMISSION INPUT SPEED SENSOR CIRCUIT (4L80-E)

Sensor consists of a permanent magnet surrounded by a coil of wire. As forward clutch housing rotates, an AC voltage is induced in circuit. Signal voltage and frequency vary directly with forward clutch rotational speed.

DTC 74 will set when

1. DTC 24, 28 or 71 is not set.
2. Transmission range not in Park or Neutral.
3. Engine speed greater than 300 RPM.
4. Transmission output speed greater than 200 RPM.
5. Transmission input speed less than 50 RPM.
6. All conditions are met for 2 seconds.

PCM will default to no TCC operation.

Note. Test numbers refer to numbers on diagnostic chart.

1. This checks entire circuit for continuity.
2. This checks output of the input speed sensor.

Check for poor connections in PCM related circuits.

DTC 74 Schematic (4L80-E) Transmission Input Speed Sensor Circuit. Scheme 197

DTC 74 Flow Chart (4L80-E) Transmission Input Speed Sensor Circuit. Scheme 198

DTC 75, SYSTEM VOLTAGE LOW

Battery voltage input circuit is battery feed for PCM. Ignition voltage input circuit is ignition feed for PCM. DTC 75 will set when ignition is on and PCM battery voltage input terminal voltage is less than graduated scale of

1. 40°F (-40°C) equals 7.3 volts with engine speed greater than 1000 RPM for 4 seconds.
2. 194°F (90°C) equals 10.3 volts with engine speed greater than 1000 RPM for 4 seconds.
3. 304°F (150°C) equals 11.7 volts with engine speed greater than 1000 RPM for 4 seconds.

Pressure control solenoid is turned off, soft landing to default 3rd gear and TCC operation is inhibited. The setting of additional DTCs may result. DTC 75 will be stored in PCM memory but will not turn on MIL.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks that normal battery voltage is 9-15 volts.
2. This test checks if low voltage display is due to generator, battery voltage input circuit or PCM, while engine is running. If voltage is less than 8.6 volts, PCM is okay.

Battery voltage input circuit supplies battery voltage to PCM. Charging battery with a battery charger and jump-starting an engine may set DTC 53. If DTC sets when an accessory is operated, check for faulty connections or excessive current draw. Check for faulty connections at starter solenoid or fusible link.

DTC 75 Flow Chart (6.5L Diesel) System Voltage Low. Scheme 199

DTC 76, RESUME/ACCEL SWITCH FAULT

Cruise ON/OFF, SET/COAST and RESUME/ACCEL switches are inputs to fuel control portion of PCM. These inputs allow PCM to control and hold a requested speed. Resume/accel request signal circuit supplies ignition voltage to PCM when resume/accel is depressed. DTC 76 will set when

1. Cruise control is on.
2. Ignition voltage on resume/accel request signal circuit is present for more than 25.5 seconds.

PCM will disallowing all cruise inputs. TCC shift schedules may be affected.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step determines if resume/accel request signal circuit is shorted to voltage.
2. This step determines if PCM or switch is at fault.

Check for RESUME/ACCEL switch stuck in engage position or for a short to voltage in resume/accel request signal circuit.

DTC 76 Flow Chart (6.5L Diesel) Resume/Accel. Switch Fault. Scheme 200

DTC 78, WASTEGATE SOLENOID FAULT

PCM operates a solenoid to control boost. This solenoid is normally open. By providing a ground path PCM energizes solenoid which then allows vacuum to pass to wastegate valve. During normal operation, PCM compares its wastegate duty cycle signal with boost signal and makes corrections in duty cycle accordingly. DTC 78 will set when

1. RPM greater than 1800.
2. Fuel rate greater than 20 mm.
3. Boost pressure greater than or less than desired (internal to PCM).

PCM will default to boost shutdown. Reduce maximum fuel.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step checks for a good vacuum source.
2. This step checks for a faulty vacuum line or pump.
3. This step checks the solenoid wiring.

A vacuum leak or a pinched vacuum line may cause DTC 78 to set. Check all vacuum lines and components connected to hose for leaks or sharp bends. Check vacuum source. DTC 32 will set if a problem exists with vacuum source. Also check for proper vacuum line routing.

DTC 78 Flow Chart (6.5L Diesel) Wastegate Solenoid Fault. Scheme 201

DTC 79, TRANSMISSION FLUID OVERTEMP - 4L60-E & 4L80-E

Transmission Fluid Temperature (TFT) sensor is a thermistor within transmission range pressure switch assembly, that controls signal voltage to PCM. PCM applies voltage on 5-volt TFT signal circuit to sensor. When transmission fluid is cold, sensor resistance is high and PCM will sense high signal voltage.

As transmission fluid temperature warms to normal transmission operating temperature of 212°F (100°C), sensor resistance becomes less and voltage decreases to 1.5-2.0 volts. DTC 79 will set when signal voltage indicates TFT greater than 295°F (146°C) for 30 seconds, and DTC 58 or 59 is not set.

DTC 79 will be stored in PCM memory but will not turn on MIL.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks for a shorted circuit or a skewed sensor.
2. This test simulates a DTC 59.

Check harness routing for a potential short to ground in 5-volt TFT signal circuit. Scan tester TFT display should rise steadily to about 212°F (100°C) then stabilize.

Test transmission fluid temperature sensor at various temperature levels to evaluate possibility of a skewed (mis-scaled) sensor. See TEMPERATURE VS. RESISTANCE VALUES table. A skewed sensor could result in delayed garage shifts or TCC complaints.

TEMPERATURE VS. RESISTANCE VALUES (1) (2)

DTC 79 Flow Chart (All Models) Transmission Fluid Overtemp. Scheme 202

DTC 81, 2-3 SHIFT SOLENOID CIRCUIT FAULT - 4L60-E & 4L80-E

Ignition voltage is supplied directly to 2-3 shift solenoid. PCM controls solenoid by providing ground path through 2-3 shift solenoid control circuit. DTC 81 will set when PCM commands solenoid on and voltage remains high for 2 seconds, or PCM commands solenoid off and voltage remains low for 2 seconds.

If solenoid is shorted off, 3rd gear only will occur. If solenoid is shorted on, 2nd gear only will occur. DTC 81 will be stored in PCM memory but will not turn on MIL.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks the function of 2-3 shift solenoid and internal transmission wiring.
2. This test checks for power to 2-3 shift solenoid from ignition, through fuse.

Check all connections at transmission. An open in ignition feed circuit can cause multiple DTCs to set.

DTC 81 Schematic (4L60-E) 2-3 Shift Solenoid Circuit Fault. Scheme 203

DTC 81 Schematic (4L80-E) 2-3 Shift Solenoid Circuit Fault. Scheme 204

DTC 81 Flow Chart (All Models) 2-3 Shift Solenoid Circuit Fault. Scheme 205

DTC 82, 1-2 SHIFT SOLENOID CIRCUIT FAULT - 4L60-E & 4L80-E

Ignition voltage is supplied directly to 1-2 shift solenoid. PCM controls solenoid by providing ground path through 1-2 shift solenoid control circuit. DTC 82 will set when PCM commands solenoid on and voltage remains high for 2 seconds, or PCM commands solenoid off and voltage remains low for 2 seconds.

PCM will only allow 2nd and 3rd gear, or 1st and 4th gear. DTC 82 will be stored in PCM memory but will not turn on MIL.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks the function of 1-2 shift solenoid and internal transmission wiring.
2. This test checks for power to 1-2 shift solenoid from ignition through fuse.

Check all connections at transmission. An open in ignition feed circuit can cause multiple DTCs to set.

DTC 82 Schematic (4L60-E) 1-2 Shift Solenoid Circuit Fault. Scheme 206

DTC 82 Schematic (4L80-E) 1-2 Shift Solenoid Circuit Fault. Scheme 207

DTC 82 Flow Chart (All Models) 1-2 Shift Solenoid Circuit Fault. Scheme 208

DTC 83, TCC PWM SOLENOID CIRCUIT FAULT - 4L60-E & 4L80-E

TCC PWM is used in combination with TCC solenoid to regulate fluid to torque converter and attached to transmission control valve body. PCM supplies a ground, allowing current to flow through solenoid coil according to duty cycle (percentage of on and off time). This current flow through solenoid coil creates a magnetic field that magnetizes the solenoid core. The magnetized core attracts the check ball to seat against spring pressure. This blocks the exhaust for the TCC signal fluid and allows 2-3 drive fluid to feed TCC signal circuit. TCC signal fluid pressure acts on TCC regulator valve to regulate line pressure and to apply fluid pressure to torque converter clutch shift valve. When TCC shift valve is in apply position, regulated fluid pressure is directed through TCC valve to apply torque converter clutch.

DTC 83 will set when

1. PCM commands solenoid on and voltage remains high (B+).

Or

1. PCM commands solenoid off and voltage remains low (zero volt).
2. All conditions are met for 2 seconds.

PCM will default to inhibit TCC operation and inhibit 4th gear operation if in hot mode.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks if PCM is commanding TCC solenoid on.
2. This test checks for voltage to solenoid.

Check all connections, especially those at transmission pass-thru connector.

DTC 83 Schematic (4L60-E) TCC PWM Solenoid Circuit Fault. Scheme 209

DTC 83 Schematic (4L80-E) TCC PWM Solenoid Circuit Fault. Scheme 210

DTC 84, ACCELERATOR PEDAL POSITION (APP) CIRCUIT FAULT

Accelerator Pedal Position (APP) module provides a voltage signal that changes relative to accelerator position. There are 3 sensors located within APP module that are scaled differently. DTC 84 will set when PCM has recognized an intermittent APP fault and there are no other current APP faults set.

When DTC 84 is set, a current and history DTC will set but will not turn on SERVICE THROTTLE SOON light, and vehicle will operate with limited power.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step determines if DTC 84 is result of a hard failure or an intermittent condition.

Check for faulty connections at APP module, PCM and instrument cluster connector.

DTC 84 Flow Chart (6.5L Diesel) Accelerator Pedal Position (APP) Circuit Fault. Scheme 211

DTC 85, UNDEFINED RATIO ERROR (4L80-E)

PCM calculates ratio based on transmission input speed and output speed sensor readings. PCM compares known transmission ratio to calculated ratio, for particular gear range selected. DTC 85 will set when

1. DTCs 21, 22, 24, 28, 71, 72 and 87 are not set.
2. TP is greater than 25 percent.
3. Not in Park/Neutral or 4th gear.
4. Engine speed is greater than 300 RPM.
5. Vehicle speed is greater than 7 MPH.
6. All conditions are met for 2 seconds.

PCM will default to line pressure set to maximum and inhibits TCC operation.

Note. Test numbers refer to numbers on diagnostic chart.

1. An out-of-range transmission range pressure switch could falsely indicate the actual transmission range.
2. This test checks calculated ratio to determine if ratio is within parameters.

DTC 85 will set when an unknown gear ratio is detected for any gear but 4th. Note commanded gear and incorrect ratio. Check transmission fluid level. Compare scan tester gear ratio reading to specifications in GEAR RATIO table.

GEAR RATIO

DTC 85 Schematic (4L80-E) Undefined Ratio Error. Scheme 212

DTC 85 Flow Chart (4L80-E) Undefined Ratio Error. Scheme 213

DTC 86, LOW RATIO ERROR (4L80-E)

PCM calculates ratio based on transmission input speed and output speed sensor readings. PCM compares known transmission ratio to calculated ratio, for particular gear range selected. DTC 86 will set when

1. DTCs 21, 22, 24, 28, 71, 72 and 74 are not set.
2. Not in Park/Neutral or Reverse.
3. TP is greater than 25 percent.
4. Engine speed is greater than 300 RPM.
5. Vehicle speed is greater than 7 MPH.
6. Trans. gear ratio is less than 1.06 in 1st or 2nd gear.
7. All conditions are met for 2 seconds.

PCM will default to 2nd gear, line pressure set to maximum and inhibits TCC operation.

Note. Test numbers refer to numbers on diagnostic chart.

1. An out-of-range transmission range pressure switch could falsely indicate actual transmission range.
2. This test compares known ratio for a commanded gear to calculated ratio displayed on scan tester.

DTC 86 will set when trans. commanded gear is 1st or 2nd and trans. is mechanically in 3rd or 4th gear. DTC 81 is used to detect a 2-3 shift solenoid circuit malfunction.

DTC 86 Flow Chart (4L80-E) Low Ratio Error. Scheme 214

DTC 87, HIGH RATIO ERROR (4L80-E)

PCM calculates ratio based on transmission input speed and output speed sensor readings. PCM compares known transmission ratio to calculated ratio, for particular gear range selected. DTC 87 will set when

1. DTCs 21, 22, 24, 28, 71, 72 and 74 are not set.
2. Not in Park/Neutral or Reverse.
3. TP is greater than 25 percent.
4. Engine speed is greater than 300 RPM.
5. Vehicle speed is greater than 7 MPH.
6. Transmission temperature is greater than 68°F (20°C).
7. Trans. gear ratio is greater than 1.42 in 3rd or 4th gear.
8. All conditions are met for 2 seconds.

PCM will default to 2nd gear, line pressure set to maximum and inhibits TCC operation.

Note. Test numbers refer to numbers on diagnostic chart.

1. An out-of-range transmission range pressure switch could falsely indicate actual transmission range.
2. This test compares known ratio for a commanded gear to calculated ratio displayed on scan tester.

DTC 87 will set when trans. commanded gear is 3rd or 4th and trans. is mechanically in 1st or 2nd gear. DTC 81 is used to detect a 2-3 shift solenoid circuit malfunction.

DTC 87 Flow Chart (4L80-E) High Ratio Error. Scheme 215

DTC 88, TDC OFFSET ERROR

This DTC indicates there is a pump timing problem. This DTC will set if TDC offset is greater than plus or minus 2 degrees, or PCM has lost memory (TDC offset is stored in PCM memory). Check injection pump timing. If okay, program TDC OFFSET into PCM. When all diagnosis and repairs are complete, clear DTCs and verify operation.

DTC'S 91-98, CYLINDER BALANCE FAULT

PCM is able to increase and decrease amount of fuel to each cylinder to provide smooth idle operation. DTCs 91-98 will set if too great of a fuel adjustment is required. These DTC's indicate a possible mechanical or fuel delivery problem. DTC's 91-98 will set when

1. Engine idling.
2. Coolant at operating temperature.
3. Cylinder fault constant.
4. Fuel correction amount exceeds defined limits (internal to PCM) for 2 seconds.

PCM will default to rough idle. DTC will be stored as a current and history code, but will not turn on MIL.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step will determine if there is a specific cylinder at fault by using cylinder out (INJ. BALANCE). If a specific cylinder is not responding to cylinder cutout (RPM drop), this cylinder should be considered a suspect cylinder.
2. This step will determine if a faulty duel mass flywheel is setting multiple cylinder balance DTCs.

To properly identify suspect cylinders, scan tester must be used. Scan tester INJ. BALANCE test will cut out specific cylinder requested. Scan tester will cut out a specific cylinder for 60 second intervals (cylinder cutout can be repeated for same cylinder as necessary). Faulty injection nozzles will set cylinder balance DTCs and should always be checked first. A nozzle can be swapped from one cylinder to another as a quick check to identify a fault.

DTC'S 91-98 Flow Chart (6.5L Diesel) Cylinder Balance Fault. Scheme 216

DTC 99, APP NO. 2 (5-VOLT REFERENCE FAULT)

Accelerator Pedal Position (APP) module provides a voltage signal that changes relative to accelerator position. There are 3 sensors located within APP module that are scaled differently. DTC 99 will set when reference voltage on APP No. 2 is less than 4.8 volts for 2 seconds. When DTC 99 is set, PCM will light SERVICE THROTTLE SOON light and limit power.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step determines there is a good 5-volt reference.

Scan tester displays APP No. 2 position in volts and should display 4.5 volts with throttle closed and ignition on or engine at idle. Voltage should decrease at a steady rate as throttle is moved toward WOT.

Monitor APP No. 2 sensor while applying accelerator pedal with engine off and ignition on. Display should vary from about 4.5 volts with throttle closed, to about 1.5 volts with throttle at WOT. DTC 99 will set if a short to ground is present in 5-volt reference circuit.

DTC 99 Flow Chart (6.5L Diesel) Accelerator Pedal Position (APP) NO. 2 (5-volt Reference Fault). Scheme 217

Wiring Diagram (6.5L Diesel VIN F & P With M/T - 1 Of 2). Scheme 218

Wiring Diagram (6.5L Diesel VIN F & P With M/T - 2 Of 2). Scheme 219

Wiring Diagram (6.5L Diesel VIN P With 4L60-E - 1 Of 2). Scheme 220

Wiring Diagram (6.5L Diesel VIN P With 4L60-E - 2 Of 2). Scheme 221

Wiring Diagram (6.5L Diesel VIN F & S With 4L80-E - 1 Of 2). Scheme 222

Wiring Diagram (6.5L Diesel VIN F & S With 4L80-E - 2 Of 2). Scheme 223

See also:
• BASIC TESTING - 6.5L DIESEL
• TESTS W/O CODES - 6.5L DIESEL
• COMPUTER RELEARN PROCEDURES
• PIN VOLTAGE CHARTS - 6.5L DIESEL
• ENTERING & EXITING DIAGNOSTIC MODE
• DTC IDENTIFICATION
• DTC 13
• DTC 14
• DTC 15
• DTC 16
• DTC 17
• DTC 18
• DTC 19
• DTC 21
• DTC 22
• DTC 23
• DTC 24
• DTC 25
• DTC 26
• DTC 27
• DTC 28
• DTC 29
• DTC 31
• DTC 32
• DTC 33
• DTC 34
• DTC 35
• DTC 36
• DTCS 37/38
• DTC 39
• DTC 41
• DTC 42
• DTC 43
• DTC 44
• DTC 45
• DTC 46
• DTC 47
• DTC 48
• DTC 49
• DTC 51
• DTCS 52/53
• DTC 54
• DTC 56
• DTC 57
• DTC 58
• DTC 59
• DTC 61
• DTC 62
• DTC 63
• DTC 64
• DTC 65
• DTC 66
• DTC 67
• DTC 68
• DTC 69
• DTC 69
• DTC 71
• DTC 72
• DTC 73
• DTC 74
• DTC 75
• DTC 76
• DTC 78
• DTC 79
• DTC 81
• DTC 82
• DTC 83
• DTC 84
• DTC 85
• DTC 86
• DTC 87
• DTC 88
• DTC 91
• DTC 99
• TRANSMISSION RANGE PRESSURE SWITCH COMBINATIONS
• EGR CONTROL PRESSURE/BARO SENSOR OUTPUT CHECK