Engine Controls - Tests W/codes - 6.5L Diesel: Other Chevrolet Suburban C1500

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)

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»(ref-20088-S24535855252001010200000) 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»(ref-20101) article.

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 218

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.

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 219

EGR Control Pressure/BARO Sensor Output Check Flow Chart (6.5L Diesel) EGR Control Pressure/BARO Sensor Output Check. Scheme 220

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 221

DTC 28 Schematic (4L80-E) Transmission Range Pressure Switch Circuit Fault. Scheme 222

DTC 28 Flow Chart (6.5L Diesel) Transmission Range Pressure Switch Circuit Fault. Scheme 223

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.

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.