Diesel Cec Tests W/codes Chevrolet Suburban C10

DESCRIPTION

The Diesel Electronic Control (DEC) system is used on California 6.2L diesel engines with light duty emissions. The DEC system monitors various engine functions to electronically control the exhaust gas recirculation (EGR) system and torque converter clutch (TCC). The Electronic Control Module (ECM) is the "brain" of the system.

Engine Speed Sensor Location (Pickup Models Only). Scheme 69

MAP Sensor Location. Scheme 70

Throttle Position Sensor Location. Scheme 71

EGR System Components and Locations. Scheme 72

Diesel Diagnostic Check Tester This tester must be used to determine system failures. Scheme 73

ALCL Connector Identification. ALCL is located under left side of dash on pickup models and under driver's seat on van models. Scheme 74

ECM Location. ECM is located under right side of dash on pickup models and under driver's seat on van models. Scheme 75

DEC System Component Locations for Trucks and Vans. Scheme 76

BASIC DIAGNOSTIC PROCEDURE

Any diagnosis of the DEC system should be performed in the following order

1. Ensure that all engine systems not related to the DEC system are operating properly. This should include a careful visual underhood inspection including: all vacuum hoses for correct routing, pinches, cuts, or disconnects; all wires in engine compartment for correct and good connections, burned or chaffed spots, pinched wires, or contact with sharp edges or hot exhaust manifolds.
2. Perform Diagnostic Circuit Check and continue diagnosis as indicated in chart. This check will either verify proper DEC system and ECM operation, or direct you to a specific trouble code chart(s) or another DEC system chart.
3. If any trouble codes are stored, start with the lowest numbered code and diagnose using the appropriate trouble code chart. If code 51, 52 or 53 are stored, always go to that chart FIRST.
4. After any repair to the DEC system, the Diagnostic Circuit Check must be repeated to verify proper system operation.

READING TROUBLE CODES

When the DDC tester is connected to the ALCL connector (ignition on and engine not running), the CEL on the tester will flash a Code 12, indicating that the ECM is operating properly and can recognize a fault in the system.

Codes are indicated by flashes of the CEL. For example, FLASH, pause, FLASH, FLASH, longer pause, identifies Code 12. This will repeat three times, followed in ascending numerical order by any stored codes (each repeated 3 times).

If no other codes are stored, the light will continue to flash Code 12. Within about 5 seconds of engine start the light should go out, indicating that the ECM has not detected a fault.

TROUBLE CODE IDENTIFICATION

ECM TROUBLE CODE IDENTIFICATION

CLEARING TROUBLE CODES

Trouble codes should be cleared when indicated in Diagnostic Circuit Check chart, and after the repair of a circuit. To clear trouble codes, the fused 12-volt source to ECM must be disconnected for 10 seconds by disconnecting the positive battery terminal or removing the "ECM B" fuse at the fuse panel.

DIAGNOSTIC CIRCUIT CHECK

Diagnostic Circuit Check determines if: 1) the ECM is operating and can recognize a fault, and 2) if any faults exist. This is the starting point for any diagnosis. If no faults are indicated, go to the Diesel Diagnostic Check (DDC) Tester Check.

Flow Chart, Diagnostic Circuit Check. Scheme 77

Flow Chart, Diagnostic Circuit Check. Scheme 78

DDC TESTER CHECK

The Diesel Diagnostic Check (DDC) Tester (J-34750) is used to check the ECM's ability to detect a fault and set a trouble code. The mode selector assists diagnostics if no code is set.

This test verifies that the DDC tester is operating properly.

Note. The following step numbers refer to the numbers in the accompanying flow chart(s).

1. Checks to see if tester is supplied with 12 volts, and if ALCL circuit is grounded or faulty. Normally, when connection is made to ALCL, the Check Engine light (CEL) in the tester should glow.
2. When ignition is turned "on", the CEL should remain on. If CEL goes off, ECM may be shorted internally.

Note. When using the DDC tester in any diagnostic mode (3.9K or 10K), the CEL will flicker. This is normal. When switching from a diagnostic mode to Normal or Ground, the CEL will glow steadily for 10 seconds, then go off. This is the normal ECM reset time.

Flow Chart, DDC Tester Check. Scheme 79

Flow Chart, DDC Tester Check. Scheme 80

ECM CHECK CEL DOESN'T FLASH CODE 12 OR REMAINS ON

This check determines why the CEL remains on or does not flash Code 12. Since the CEL is remote from the ECM, it can recognize faulty ECM power or ECM.

Note. The following step numbers refer to the numbers in the accompanying flow chart(s).

1. Checks for proper CEL signal (approximately battery voltage) at ALCL.
2. Checks for 12 volts at ECM ignition feed terminals.
3. Checks for good ECM ground. If ECM power and ground terminals are OK, check ECM-to-connecter terminal connections.
4. When vehicle is started, ECM turns CEL off. Voltage at ALCL should drop below 6 volts.

Chart, ECM Check CEL Doesn't Flash Code 12 Or Remains On. Scheme 81

Chart, ECM Check CEL Doesn't Flash Code 12 Or Remains On. Scheme 82

EPR SOLENOID ELECTRICAL CHECK

EPR solenoid controls vacuum to EPR valve. The EPR solenoid, when energized, allows vacuum pump vacuum to close EPR valve and increase exhaust back pressure for proper EGR operation. Solenoid power (12V) is supplied by the ignition and grounded through the ECM, energizing the solenoid and turning EPR on.

Note. The following step numbers refer to the numbers in the accompanying flow chart(s).

1. Checks for short to ground or faulty ECM signal to solenoid. Test light should be off.
2. Checks for signal to energize EPR solenoid with engine idling. If test light is on, electrical circuits to solenoid are OK.
3. Checks for ignition voltage or open circuit from terminal "B" to ECM, terminal "C12".

Flow Chart, EPR Solenoid Electrical Check. Scheme 83

Flow Chart, EPR Solenoid Electrical Check. Scheme 84

EPR VACUUM CHECK

The EPR solenoid controls vacuum to EPR valve. The EPR solenoid, when energized, allows vacuum pump vacuum to close EPR valve and increase exhaust back pressure for proper EGR operation. The EPR valve is a combination vacuum actuator and exhaust restrictor plate. When vacuum is applied to the actuator, the restrictor plate closes, increasing exhaust system back pressure and allowing the EGR valve to function more efficiently.

Note. The following step numbers refer to the numbers in the accompanying flow chart(s).

1. Checks for normal EPR vacuum at idle. Electrical circuit was verified as OK on prior chart. Absence of vacuum here is due to source failure (vacuum pump) or a restricted/leaking vacuum line to the valve.
2. Checks to see if solenoid will respond to ECM command.
3. Checks for normal operation of EPR valve.

Note. See EPR Solenoid Electrical Check for wiring.

Flow Chart, EPR Vacuum Check. Scheme 85

Flow Chart, EPR Vacuum Check. Scheme 86

TCC CHECK

The Torque Converter Clutch (TCC) eliminates power loss during highway cruise conditions. An ECM controlled solenoid in the transmission activates the TCC.

Ignition power is supplied to the solenoid through a brake switch which opens when the brake is applied. The ECM completes the ground to activate the TCC solenoid for clutch engagement.

Note. The following step numbers refer to the numbers in the accompanying flow chart(s).

1. Checks for complete circuit from ignition through solenoid to the test point.
2. Checks that the ECM is completing the circuit to ground to engage the TCC.
3. Checks for TPS signal to ECM.
4. Checks ground circuit to ECM terminal "A2".
5. Checks for ignition voltage to terminal "A" of the TCC harness connector.
6. Checks for complete circuit from ignition to ground via TCC test terminal in ALCL.

Flow Chart, TCC Check. Scheme 87

Flow Chart, TCC Check. Scheme 88

COLD ADVANCE CONTROL CHECK

The cold advance control (CAC) circuit is designed to advance injection timing about 4° during cold operation. The circuit is activated by a temperature switch through a cold advance control relay to a cold advance solenoid. The switch is calibrated to open the circuit at coolant temperatures above 95°F (35°C).

Below 95°F (35°C), with the ignition switch "on", the cold advance solenoid is continuously energized without the engine running. Below this temperature, with the engine running, a timer in the relay starts to operate and closes the circuit to the cold advance solenoid for 35 seconds. When the solenoid is energized and the engine is running, housing pressure is decreased from 10 psi (69 kPa) to zero which advances the timing 4 degrees.

After 35 seconds, the cold advance solenoid is de-energized and the housing pressure is returned to 10 psi (69 kPa).

Flow Chart, Cold Advance Control Check. Scheme 89

Flow Chart, Cold Advance Control Check. Scheme 90

CODE 12 - NO REFERENCE PULSE

Code 12 means ECM is on, but sees no reference pulse from Engine Speed Sensor (normal condition with ignition on and engine not running). Code 12 does not store, and will only flash when fault is present. With engine running, Code 12 could mean an open or ground in sensor reference circuit.

The sensor receives a 5-volt reference signal and pulses this signal back to the ECM 4 times per revolution. The ECM measures engine RPM by counting these pulses.

Note. The following step numbers refer to the numbers in the accompanying flow chart(s).

1. Checks for a good 5-volt reference signal.
2. Checks for proper ECM voltage to Engine Speed Sensor. If circuit to ECM is complete, normal voltage will be about 5 volts with harness disconnected from sensor.
3. Checks for good sensor ground circuit (452) to ECM. Indicates whether open indicated in step 2) is in wire or at ECM.

Flow Chart, Code 12, No Reference Pulse. Scheme 91

Flow Chart, Code 12, No Reference Pulse. Scheme 92

CODE 21 - TPS OPEN OR MISADJUSTED

The Throttle Position Sensor (TPS) is a variable resistor that supplies the ECM with throttle opening information. The sensor is supplied with a 5-volt reference signal. Sensor resistance is lowest (high signal to ECM) at wide open throttle.

Code 21 means that the ECM has seen high voltage at terminal "A2" for more than 30 seconds with engine speed below 1120 RPM.

Note. The following step numbers refer to the numbers in the accompanying flow chart(s).

1. Checks to confirm if Code is still present.
2. Checks reference voltage at TPS harness connector to determine whether problem is in electrical circuit or TPS.
3. Checks to see if low reference voltage is due to a grounded wire or ECM.

Flow Chart, Code 21, TPS Open Or Misadjusted. Scheme 93

Flow Chart, Code 21, TPS Open Or Misadjusted. Scheme 94

CODE 22 - TPS GROUNDED OR MISADJUSTED

The Throttle Position Sensor (TPS) is a variable resistor that supplies the ECM with throttle opening information. The sensor is supplied with a 5-volt reference signal. Sensor resistance is highest (low signal to ECM) at closed throttle.

Code 22 means that the ECM has seen low voltage at terminal "A2" for more than 2 minutes with engine speed over 1250 RPM.

Note. The following step numbers refer to the numbers in the accompanying flow chart(s).

1. Confirms that code is still present.
2. Checks for reference voltage at TPS harness connector to determine whether problem is electrical circuit or faulty TPS. If circuit is OK, normal voltage reading will be about 5 volts.

Flow Chart, Code 22, TPS Grounded Or Misadjusted. Scheme 95

Flow Chart, Code 22, TPS Grounded Or Misadjusted. Scheme 96

CODE 24 - VEHICLE SPEED SENSOR

The ECM applies and monitors a 12-volt signal on circuit 437. This circuit is alternately grounded by the Vehicle Speed Sensor (VSS) as the drive wheels turn. The ECM interprets the time between these pulses (about 2000 per mile) as vehicle speed.

Code 24 indicates that the ECM has seen a vehicle speed signal of less than 10 MPH for more than 10 seconds with engine speed over 200 RPM.

Note. The following step numbers refer to the numbers in the accompanying flow chart(s).

1. This test monitors ECM voltage on circuit 437. With wheels turning, pulsing action will result in voltage signal variation which decreases with increased speed to an average of 4-6 volts at 20 MPH.
2. Voltage of less than 1 volt at the ECM connector indicates that circuit 437 is shorted to ground. Disconnect circuit 437 at the VSS. If voltage now reads about 10 volts, the VSS is faulty. If voltage remains less than 10 volts, then circuit 437 is grounded. If 437 is not grounded, check for a faulty ECM connector or ECM.
3. A steady 8-12 volts at the ECM connector indicates an open in circuit 437 or a faulty VSS.
4. Normal voltage condition (indicates a possible intermittent condition).

Flow Chart, Code 24, Vehicle Speed Sensor. Scheme 97

Flow Chart, Code 24, Vehicle Speed Sensor. Scheme 98

CODE 31 - MAP SENSOR VOLTAGE TOO LOW

The Manifold Absolute Pressure (MAP) sensor monitors the amount of vacuum in EGR circuit. If MAP sensor indicates a different vacuum signal than that calculated by the ECM (based on EGR duty cycle), the ECM makes minor corrective adjustments. If a significant difference is noted, ECM recognizes fault, sending a full EGR signal.

Note. The following step numbers refer to the numbers in the accompanying flow chart(s).

1. Checks to confirm a code is still present.
2. Checks to determine if EGR valve is receiving vacuum.
3. Checks for 5-volt reference signal to MAP sensor.
4. Checks for 5-volt reference at the ECM.
5. Checks for an open in the EGR solenoid circuit.

Flow Chart, Code 31, MAP Sensor Voltage Too Low. Scheme 99

Flow Chart, Code 31, MAP Sensor Voltage Too Low. Scheme 100

CODE 32 - EGR LOOP ERROR

Under normal operating conditions, the ECM compares EGR duty cycle signal with absolute pressure signal indicated by MAP sensor. If MAP sensor signal is different from that calculated by the ECM (based on EGR duty cycle) for 10 seconds or more, a Code 32 will set and the ECM will shut down EGR.

Note. The following step numbers refer to the numbers in the accompanying flow chart(s).

1. Checks to determine if Code 32 can reset.
2. If Diagnostic Circuit Check indicated Code 32, there is probably a minor vacuum leak in the vacuum circuit.

Flow Chart, Code 32, EGR Loop Error. Scheme 101

Flow Chart, Code 32, EGR Loop Error. Scheme 102

CODE 33 - MAP SENSOR VOLTAGE TOO HIGH

The Manifold Absolute Pressure (MAP) Sensor monitors the amount of vacuum in the EGR circuit. If the MAP sensor indicates a different vacuum signal than that calculated by the ECM (based on EGR duty cycle), the ECM makes minor corrective adjustments. If a significant difference is noted, the ECM recognizes a fault and sends a full EGR signal.

Note. The following step numbers refer to the numbers in the accompanying flow chart(s).

1. Checks to confirm a code is still present.
2. Checks to determine if solenoid is stuck closed.
3. Checks for short to ground in either solenoid circuit, or fault in ECM.

Flow Chart, Code 33, MAP Sensor Voltage Too High. Scheme 103

Flow Chart, Code 33, MAP Sensor Voltage Too High. Scheme 104

CODE 51 - FAULTY PROM

1. Check that all pins are fully inserted in the socket.
2. If OK, replace PROM, and recheck.
3. If problem not corrected, replace ECM.

CODE 52 - FAULTY ECM

1. Check that ECM connectors are fully inserted.
2. Clear memory.
3. DDC Tool connected and in "Normal" mode.
4. Start engine and check for light.
5. If light reappears and DDC Tool indicates code 51, replace ECM.
6. Clear memory after repair to confirm no "CEL".

CODE 53 - REFERENCE VOLTAGE OVERLOAD

Note. The following step numbers refer to the numbers in the accompanying flow chart(s).

1. Checks to confirm a code is still present.
2. Checks to determine if there is a 5-volt reference signal from the ECM.
3. Checks for short to ground in circuit "A12" or ECM.

Flow Chart, Code 53, Reference Voltage Overload. Scheme 105

Flow Chart, Code 53, Reference Voltage Overload. Scheme 106

6.2L Diesel ECM Terminal Identification. Scheme 107

6.2L Diesel DEC System Wiring Diagram. Scheme 108