Engine Controls - Tests W/codes - 6.5L Diesel: Other Chevrolet Pickup K2500

SCAN TESTER USAGE

Note. Before connecting scan tester, check diagnostic system and ensure accurate information is received by scan tester. Perform DIAGNOSTIC SYSTEM CHECK . If vehicle does not pass diagnostic 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 TYPICAL TECH-1 DATA VALUES .

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. 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 TYPICAL TECH-1 DATA VALUES .

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, 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.

TYPICAL TECH-1 DATA VALUES

TDC OFFSET PROGRAM PROCEDURE

This procedure allows PCM memory to be updated with correct TDC offset for vehicle. DTC 88 will be stored until procedure has been completed.

1. Battery must be fully charged, engine operating at idle and vehicle at operating temperature.
2. Connect Tech 1 scan tool. Select "OUTPUT TESTS" and "INJ. PUMP". Activate "TDC LEARN." NOTE: It will take PCM 20 seconds to learn TDC offset.
3. Verify "TDC OFFSET" in data list. DTC will be stored if procedure has not been done correctly.
4. If PCM fails to program TDC OFFSET, do the following: Check all PCM connection. Check Techline terminal/equipment for latest software version. Try again to program PCM. If it fails again replace PCM.

CHART A-1 - NO MIL (SERVICE ENGINE SOON LIGHT)

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 is blown, see «WIRING DIAGRAMS»(ref-19760-S14829851822001010200000) 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»(ref-19767) article in this section.

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

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, or no engine speed sensor signal on the diesel.

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, then the 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 the serial data circuit is okay, the PROM, PCM or SIR DERM may be at fault for the NO DLC symptom.
2. If light goes off when PCM connector is disconnected, then the 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. The problem is a faulty PROM. If DTC 12 does not flash, the PCM should be replaced using the original PROM. Replace PROM only after trying a PCM. A defective PROM usually is an unlikely cause of the problem.

Chart A-2 Flow Chart ("C" & "K" Series) No Scan Data, MIL (Service Eng. Soon) On All Times Or Will Not Flash. Scheme 376

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 the 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 the PCM.
2. This step will check to see if there is an inject command coming from the PCM.
3. This step will check the ground circuit.

EGR CONTROL PRESSURE/BARO SENSOR OUTPUT CHECK

An EGR control pressure/BARO sensor monitors the amount of vacuum in the EGR circuit. It senses actual vacuum in the EGR vacuum line and sends a signal back to the PCM. The signal is compared to the EGR duty cycle calculated by the 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 the 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 value 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 leaking or restriction. Ensure no other vacuum devices are connected to the 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 Pressure/Baro Sensor Output Check Schematic ("C" & "K" Series. Scheme 377

EGR Control Pressure/Baro Sensor Output Check Flow Chart ("C" & "K" Series). Scheme 378