Engine Controls - Tests W/codes - Electronic Transmission: Other Chevrolet Pickup C3500

SCAN TESTER USAGE

Note. Before connecting scan tester, check diagnostic circuit or system and ensure accurate information is received by scan tester. Perform DIAGNOSTIC CIRCUIT CHECK (GASOLINE) in BASIC TESTING - GASOLINE article in the ENGINE PERFORMANCE section. Perform DIAGNOSTIC SYSTEM CHECK (DIESEL) in TESTS W/CODES - 6.5L DIESEL . If vehicle does not pass diagnostic circuit or 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 SCAN TESTER DATA .

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. Code 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 SCAN TESTER DATA .

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.

SCAN TESTER DATA

Note. Information contained in the following table is typical of readings taken on vehicle with engine idling, upper 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.

SCAN TESTER DATA

CODE 24, VSS TRANS OUTPUT SIGNAL - "C" & "K" SERIES DIESEL

Note. For Code 24 coverage on gasoline models, see appropriate G - GASOLINE TESTS W/ CODES article below.

1. «TESTS W/CODES - 4.3L»(ref-19732)
2. «TESTS W/CODES - 5.0L»(ref-19750)
3. «TESTS W/CODES - 5.7L»(ref-19751)
4. «TESTS W/CODES - 7.4L»(ref-19752)

VSS output sensor is a magnetic induction type. Gear teeth pressed on outside diameter of output carrier assembly induce an alternating current in sensor when drive wheels are turning. Since vehicle speed is taken from transfer case on 4WD vehicles, output speed sensor signal on these units goes directly to PCM. Code 24 will set if gear selector is not in Park or Neutral, engine speed is at least 3000 RPM and output speed is less than 250 RPM for at least 1.5 seconds.

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

1. Test verifies VSS voltage at PCM.
2. Test checks VSS buffer ground circuit.
3. Test checks VSS circuit at buffer module.
4. Test verifies VSS signal at sensor.

CODE 28, TRANSMISSION RANGE PRESSURE SWITCH

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 the 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. Code 28 will set when range signals "A" and "C" are both zero volts (on) for 2 seconds.

Note. Test numbers refer to numbers on diagnostic chart.

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

CODES 37/38, TCC BRAKE SWITCH ON/OFF

The normally closed brake switch supplies battery voltage to the PCM. Signal voltage will drop to zero volts when brake pedal is applied.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks if voltage is available at brake switch.
2. Checks brake switch function.
3. Checks circuit from brake switch to PCM.

CODE 39, TCC STUCK OFF

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks the mechanical status of the TCC. When PCM commands the TCC solenoid off, TCC slip speed should increase.

CODE 52/53, SYSTEM VOLTAGE HIGH

Code 53 will set when ignition is on and PCM/TCM 12-volt battery feed voltage is greater than 19.5 volts for about 2 seconds. During the time the failure is present, the force motor is turned off, transmission immediately shifts to 2nd gear, and TCC operation is inhibited. The setting of additional codes may result.

Jump-starting engine or charging battery with a battery charger may set code. If code is set when an accessory is operated, check for poor connections or excessive current draw. Also, check for poor connections at starter solenoid or fusible link.

CODE 66, 3-2 CONTROL SOLENOID CIRCUIT FAULT

The 3-2 control solenoid hydraulically coordinates the apply rate of the 2-4 band with hydraulic release of the 3-4 clutch during a 3-2 downshift. 3-2 circuit duty cycle is continually monitored by the PCM depending on the command state of the circuit. When the transmission is in 1st gear the duty cycle of the solenoid is equal to zero. When the transmission is in 2nd gear or higher, the duty cycle of the solenoid will be about 90 percent. When the transmission downshifts 3-2, the duty cycle of the solenoid will be about 20 percent.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks 3-2 control solenoid and internal transmission harness for short circuits.
2. This test checks for power, from the ignition through the fuse, to the 3-2 control solenoid.

CODE 67, TCC SOLENOID CIRCUIT CHECK

The TCC solenoid is a normally open exhaust valve. The PCM will engage the solenoid by grounding circuit with an internal quad-driver.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks the ability of PCM to control solenoid.
2. This test checks for power, from the ignition through the fuse, to the TCC solenoid.

CODE 68, OVERDRIVE RATIO ERROR

The PCM/TCM monitors the difference in engine RPM and input shaft RPM. With transmission in Drive, scan tester reading should show engine speed closely matching input speed.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks the indicated range signal to the selected range. A faulty switch could set this code.
2. Checks TCC for slippage while in a commanded lock-up state.

CODE 72, VSS CKT LOSS TRANSMISSION OUTPUT SIGNAL - DIESEL

Note. For Code 72 coverage on gasoline models, see appropriate G - GASOLINE TESTS W/ CODES article in the ENGINE PERFORMANCE section. See below.

1. «TESTS W/CODES - 4.3L»(ref-19732)
2. «TESTS W/CODES - 5.0L»(ref-19750)
3. «TESTS W/CODES - 5.7L»(ref-19751)
4. «TESTS W/CODES - 7.4L»(ref-19752)

VSS output sensor is a magnetic induction type. Gear teeth pressed on outside diameter of output carrier assembly induce an alternating current in sensor when drive wheels are turning.

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

1. Test verifies VSS voltage at PCM.
2. Test checks VSS buffer ground circuit.
3. Test checks VSS circuit at buffer module.
4. Test verifies VSS signal at sensor.

CODE 73, PRESSURE CONTROL SOLENOID (CURRENT ERROR)

Note. This flow chart requires the use of a bidirectional (Tech 1) scan tester.

The pressure control solenoid, is a PCM/TCM-controlled device used to regulate transmission line pressure. The PCM/TCM looks at TPS voltage, engine RPM and other inputs to determine appropriate line pressure for a given load, then regulates the pressure by applying a varying amperage. The applied amperage can vary from 1 to 1.1 amps. The PCM/TCM then monitors amperage at the return line.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks the ability of the PCM/TCM to command the solenoid.
2. Checks internal transmission harness and solenoid for incorrect resistance.

CODE 74, TRANSMISSION INPUT SPEED ERROR

Sensor is a permanent magnet type. When rotating trigger teeth pass sensor, an AC voltage signal is produced. Signal voltage and frequency varies with forward rotational speed.

Note. Test numbers refer to numbers on diagnostic chart.

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

CODE 75, SYSTEM VOLTAGE LOW

Code 75 will set when ignition is on and PCM/TCM 12-volt battery feed voltage is less than 9 volts for about 4 seconds. During the time failure is present, force motor, also referred to as pressure control solenoid, is turned off, maintaining only 2nd gear, and inhibiting TCC operation.

NOTE ON INTERMITTENTS

If code sets when an accessory is operated, check for poor connections or excessive current draw. Also, check for poor connections at starter solenoid or fusible link. Minimum voltage allowed for Code 75 to set is on a graduated scale and changes with temperature. Minimum voltage at -40°F (-40°C) is 6.7 volts. Minimum voltage at 304°F (150°C) is 10.5 volts, and minimum voltage at 194°F (90°C) is 9 volts.

CODE 81, TRANSMISSION 2-3 ERROR

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks function of 2-3 shift solenoid and internal transmission wiring.
2. Checks for power to 2-3 shift solenoid from ignition.

CODE 82, TRANSMISSION 1-2 ERROR

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks 1-2 shift solenoid and internal transmission wiring harness for short circuits.
2. This test checks for power, from the ignition through the fuse, to the shift solenoid.

CODE 83, TCC SOLENOID CIRCUIT FAULT

The PCM/TCM continually monitors voltage on each circuit connected to the quad-driver for either low or high voltage, depending on the commanded state of the device connected to it. Code 83 will set if PCM/TCM detects an inappropriate reading on the TCC circuit. For example, if the TCC duty cycle is zero, but voltage on the TCC circuit drops as if the solenoid were on, then Code 83 will set. The TCC solenoid, because of its large current draw, is connected to 2 terminals of a single quad-driver.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks if PCM/TCM is commanding TCC solenoid on.
2. This test checks for voltage in the solenoid.

CODE 85, UNDEFINED GEAR RATIO

While in each gear, PCM/TCM calculates actual gear ratio from input and output speed readings, also referred to as vehicle speed, then compares these to what gear ratio should be, taking into consideration selected gear range. This monitor includes reverse gear, but does not include overdrive gear.

Note. Test numbers refer to numbers on diagnostic chart.

1. An out-of-calibration transmission range pressure switch could falsely set Code 85.
2. This test verifies the proper ratio.

CODE 86, LOW GEAR RATIO ERROR

Control module calculates ratio based on the transmission input speed and output speed sensor readings. Control module compares known ratio to the calculated ratio.

Note. Test numbers refer to numbers on diagnostic chart.

1. An out-of-calibration transmission range pressure switch could falsely indicate actual transmission range.
2. This test verifies the proper ratio.

CODE 87, HIGH GEAR RATIO ERROR

Control module calculates ratio based on the transmission input speed and output speed sensor readings. Control module compares known ratio to the calculated ratio.

1. An out-of-calibration transmission range pressure switch could falsely indicate actual transmission range.
2. This test verifies the proper ratio.