Engine Controls - Tests W/codes - Gasoline: Other Oldsmobile Silhouette I

Hard Failures

Hard failures cause SERVICE ENGINE SOON light to illuminate and remain on until the malfunction is repaired. If light comes on and remains on (light may flash) during vehicle operation, cause must be found using diagnostic (code) charts. If a sensor fails, control unit will use a substitute value in its calculations to continue engine operation. In this condition, vehicle is functional, but driveability can be poor.

Intermittent Failures

Intermittent failures cause SERVICE ENGINE SOON light to flicker or illuminate and go out about 10 seconds after the intermittent fault goes away. The corresponding trouble code; however, will be retained in ECM memory. If related fault does not reoccur within 50 engine restarts, it will be erased from ECM memory. Intermittent failures may be caused by faulty sensor, connector or wiring. See INTERMITTENTS in TESTS W/O CODES article in this section.

Field Service Mode Check

SERVICE ENGINE SOON light indicates operational mode of engine if ALDL is grounded while engine is running. Light response confirms proper fuel system operation and verifies closed loop operation. Clear codes and perform this test after any repair is completed. Field service mode check can be found by proceeding to FIELD SERVICE MODE CHECK in BASIC TESTING article in this section.

SCAN TESTER USAGE

Note. Before connecting scan tester, check diagnostic system and ensure accurate information is received by scan tester. Perform DIAGNOSTIC CIRCUIT CHECK in BASIC TESTING article in this section. If vehicle does not pass diagnostic circuit 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 back-probe 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 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 ECM. 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 ALDL 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 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 ALDL test terminal. If same codes are not flashed by SERVICE ENGINE SOON light as were indicated by scan tester, tester cannot be used on vehicle and information obtained by it will not be guaranteed accurate.

SCAN 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). Data parameters are updated every 1 1/2 seconds. Not all devices and systems are used on all models. For additional information, see tester owner's manual.

SCAN TESTER DATA

SUMMARY

If hard fault codes are not present and driveability symptoms or intermittent codes exist, proceed to TESTS W/O CODES article in this section for diagnosis by symptom (i.e. ROUGH IDLE, NO START, etc.), or intermittent diagnostic procedures.

Note. The following diagnostic flow charts and mini-schematics are supplied courtesy of General Motors Corp.

CODE 13, OPEN OXYGEN SENSOR CIRCUIT

When exhaust temperature is less than 600°F (316°C), O2 sensor is open and produces no voltage. An open sensor circuit or cold sensor will not allow system to entire closed loop.

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

1. Code 13 will set at normal operating temperature if at least 2 minutes have passed since engine start, Code 21 or 22 is not present, O2 signal voltage is steady at .35-.55 volt and throttle position sensor signal is greater than idle. All conditions must be met for at least one minute.
2. This determines if fault is in O2 sensor, ECM or wiring.
3. Use only a high-impedance Digital Volt-Ohmmeter (DVOM) while checking for continuity in signal and ground circuits. If ground circuit is open, voltage on signal circuit will be greater than .6 volt.

CODE 14, COOLANT SENSOR SIGNAL VOLTAGE LOW

ECM uses coolant temperature sensor inputs in determining control of fuel delivery, engine timing (EST), idle (IAC) and converter clutch (TCC). As engine warms, sensor resistance reduces. At normal operating temperature, voltage signal will be about .5-1.1 volts (4.3L Turbo) or 1.5-2.0 volts (all other models) at ECM coolant sensor signal terminal.

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

1. This tests if code was set because of a hard failure or intermittent condition. Code 14 sets if signal voltage indicates a coolant temperature greater than 275°F (135°C) for more than 3 seconds on 4.3L Turbo or 6 seconds on all other models.
2. This simulates conditions for a Code 15. If ECM recognizes open circuit by displaying a low temperature, ECM and wiring are not at fault.

CODE 15, COOLANT SENSOR SIGNAL VOLTAGE HIGH

As engine warms, sensor resistance reduces and voltage drops. At normal operating temperature, voltage signal will be about .5-1.1 volts (4.3L Turbo) or 1.5-2.0 volts (all other models) at ECM coolant sensor signal terminal. If sensor signal circuit opens, ECM will see -40°F (-40°C) and deliver fuel for this temperature.

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

1. This checks if code was set as a result of a hard failure or intermittent condition. Code 15 will set if engine is running for more 50 seconds and signal voltage indicates a coolant temperature less than -22°F (-30°C) for more than 30 seconds.
2. This simulates conditions for a Code 14. If ECM recognizes grounded circuit and displays a high temperature, ECM and wiring are okay.
3. This determines if problem is ECM or wiring. There should be 5 volts present at sensor when measured with a DVOM.

CODE 16, SYSTEM VOLTAGE HIGH/LOW 3.8L

Control module monitors battery voltage on battery feed circuit. If control module detects battery voltage greater than 17 volts or less than 9 volts for more than 10 seconds, it will set a Code 16 in memory.

Note. Test number refers to number on diagnostic chart. Starting engine with battery charger connected may set Code 16.

1. Test alternator output to determine proper operation of voltage regulator. Increase engine speed to moderate level. Measure voltage across battery terminals. If reading is more than 17 volts or less than 9 volts, service alternator.

CODE 17, rpm signal problem 3.8l

Note. Test numbers refer to numbers on diagnostic chart.

1. Verifies spark reference circuit is not shorted to ground or open in ignition jumper harness.
2. If a window on harmonic balancer is lined up with 18X Hall Effect switch, ignition module will ground spark reference signal. Starter may have to be bumped several times to obtain a voltage reading.
3. Voltage reading should be lower than reading obtained with engine not running, indicating a pulsed reference signal.

CODE 18, CAM/CRANK ERROR 3.8l

During cranking, ignition module monitors dual crank sensor sync signal. Sync signal is used to determine correct cylinder pair to spark first. After synch signal has been processed by ignition module, module sends a fuel control reference pulse to PCM. When PCM receives this pulse, it will command all 6 injectors to fire for one priming shot of fuel. After priming, all injectors are held off for 2 crankshaft revolutions to allow cylinder to use fuel from priming shot. After firing, PCM begins to operate injectors in sequential mode based upon true camshaft position. PCM expects to see 6 fuel control pulses for each cam pulse. If sequence of these pulses is incorrect 10 times consecutively, Code 18 will set.

Note. Test numbers refer to numbers on diagnostic chart.

1. Determines if conditions necessary to set code still exist.
2. If 5 volts are not present at PCM harness connector terminal, cam sensor may be interfacing with magnet in camshaft sprocket. Bumping starter should correct this problem.
3. If a failure is induced in fuel control reference circuit, 5 volts on circuit should change when faulty wiring or connection is manipulated.

CODE 21, TPS SIGNAL VOLTAGE HIGH

Throttle Position Sensor (TPS) provides a varying voltage signal depending on throttle valve angle. Signal voltage varies from about .50 volt at idle to 4.5 volts at wide open throttle. On models with non-adjustable TPS, each time TPS voltage drops to less than 1.25 volts and stops, ECM assumes this is zero degrees throttle angle and measures throttle percentage angle from this point.

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

1. This test confirms Code 21 and checks if fault is a hard failure or an intermittent condition. Code 21 will set if TPS voltage is greater than 2.5 volts 2-10 seconds with engine running. On 2.8L, Code 21 may set if MAP sensor signal less than 2 volts.
2. This test simulates conditions for Code 22. If ECM recognizes low voltage signal and sets Code 22, ECM and power and signal circuits are not at fault.
3. This step isolates a faulty sensor, ECM or an open ground circuit.

CODE 22, TPS SIGNAL VOLTAGE LOW

Throttle Position Sensor (TPS) provides a varying voltage signal depending on throttle valve angle. Signal voltage varies from less than about .50 volt at idle to 4.5 volts at wide open throttle.

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

1. This test confirms Code 22 and tests if fault is a hard failure or an intermittent condition. Code 22 will set if engine is running, TPS voltage is less than .2 volt for 2-4 seconds.
2. This simulates Code 21. If ECM recognizes a high voltage signal and sets Code 21, ECM and wiring are not at fault. On 2.8L, check and adjust TPS. On all others, replace TPS.
3. This simulates a high voltage signal to check for on open TPS signal circuit.

CODE 24, VEHICLE SPEED SENSOR (3.1L)

ECM applies and monitors a 12-volt signal on circuit No. 437 to Vehicle Speed Sensor (VSS). VSS is connected to speed sensor buffer which alternately grounds and opens circuit No. 437 when wheels are turning. This pulsing action takes place about 2000 times per mile. Voltage level and pulses increase with vehicle speed. ECM converts pulsing voltage to MPH. ECM uses VSS information in calculations to determine vehicle adjustments. Scan tester reading should closely match speedometer reading when wheels are turning.

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

1. A Code 24 sets when MPH is less than 2 MPH, transmission is not in Park or Neutral, engine speed is greater than 1400 RPM, TPS is greater than 5 percent, circuit No. 437 voltage is constant and all of these conditions are met for 30 seconds. These conditions are met during a road load deceleration.
2. A steady 8-12 volts at ECM connector indicates VSS circuit is open or speed sensor is faulty. A voltage of less than one volt at IP connector indicates circuit No. 437 wire is shorted to ground. Disconnect vehicle speed sensor connector. If voltage is now greater than 10 volts, vehicle speed sensor buffer is faulty. If voltage remains less than 8 volts, circuit is grounded. If circuit is not grounded, check for faulty ECM connector or ECM. Before replacing ECM, PROM should be checked for correct application.

CODE 24, VEHICLE SPEED SENSOR (VSS) 3.8L

Speed sensor, which is a Permanent Magnet (PM) generator, provides control module with vehicle speed information. PM generator, mounted in transmission, produces a pulsing AC voltage signal whenever vehicle speed is greater than 3 MPH. Voltage level and pulses increase with vehicle speed. Control module converts pulsing voltage to MPH, which is used by control module to calculate vehicle adjustments.

Note. Test numbers refer to numbers on diagnostic chart.

1. PM generator only produces a voltage signal if drive wheels are turning greater than 3 MPH.
2. Before replacing control module, MEM-CAL should be checked for correct application.

CODE 26, QUAD-DRIVER CIRCUIT 3.8L (1 OF 3)

Each PCM Quad-Driver Module (QDM) has a fault line which is monitored by PCM. PCM compares voltage values of fault line with acceptable values in PCM memory. If PCM senses values other than accepted values, a Code 26 will set.

Some QDM circuits will normally cycle between high and low, such as depressing brake pedal. Some scan testers may set a false Code 26 if engine is running, tester is installed and brake pedal is depressed for more than 30 seconds.

Note. Test number refers to number on diagnostic chart.

1. PCM does not know which controlled circuit set Code 26, so this chart checks each circuit to determine which is at fault. This step tests SERVICE ENGINE SOON light driver and circuit.

CODE 26, QUAD-DRIVER CIRCUIT 3.8L (2 OF 3)

Note. Test number refers to number on diagnostic chart.

1. 2) This determines which circuit is out of specification. All terminals except GC7 should have battery voltage with ignition on, engine not running and ALDL test terminal not grounded.

CODE 26, QUAD-DRIVER CIRCUIT 3.8L (3 OF 3)

Note. Test number refers to number on diagnostic chart.

1. 3) This determines if problem is circuit or component. Factory-installed PCM has an internal fuse and is unlikely to need replacement.

Scheme 115

CODE 31, PARK/NEUTRAL SWITCH CIRCUIT 3.8L

Note. Complete diagnosis of Code 31 for 3.8L requires GM Tech 1 scan tester, which is capable of indicating status of all 4 park/neutral switch positions. This chart does not apply to 3.8L (VIN L) "C", "E" and "H" body vehicles. Schematics for these models are supplied for reference purposes only.

Park/neutral switch contacts are part of neutral start switch. Contacts close to ground in Park or Neutral and open in Drive. Code 31 will set if park/neutral signal circuit indicates an open for 3 consecutive starts or if conditions occur as follows with ignition on and engine off.

1. Vehicle speed is zero MPH.
2. Gear selector switch indicates a gear other than Park or Neutral.
3. Gear selector status indicates an incorrect combination of LO and HI for more than 10 seconds.

Code 31 does not turn on SERVICE ENGINE SOON light.

Note. Test numbers refer to numbers on diagnostic chart.

1. & 2) This tests for proper operation of gear selector switch.
2. Tests for an open of grounded circuit.

CODE 32, EGR SYSTEM ERROR (3.1L)

ECM operates a Electronic Vacuum Regulator Valve (EVRV) to control vacuum to EGR valve. Regulator normally allows only a small amount of vacuum to pass to EGR valve. When ECM grounds EVRV drive circuit, EVRV opens, allowing enough vacuum to pass through to open EGR valve. ECM monitors EGR effectiveness by periodically checking fuel integrator counts. This is done when vehicle speed is greater than 50 MPH, MAP sensor signal indicates cruise condition and throttle position are constant and all conditions have been met twice for 60 seconds.

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

1. With ignition on and engine off, EVRV should not be energized or allow enough vacuum through to open EGR valve. When test terminal "B" of ALDL connector is grounded, EVRV will energize, allowing vacuum to EGR valve.
2. Checks for plugged EGR passages. If passages are plugged, engine may have severe detonation on acceleration.

Scheme 116

Scheme 117

CODE 33, MAP SENSOR SIGNAL VOLTAGE HIGH

Manifold Absolute Pressure (MAP) sensor responds to changes in manifold pressure (vacuum). If MAP sensor fails, ECM will substitute a fixed MAP value and use TPS input to control fuel delivery.

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

1. This test confirms Code 33 and determines if it is a hard failure or an intermittent condition. Code 33 will set when voltage signal reading is too high and TPS voltage indicates throttle is closed.
2. This step simulates conditions for a Code 34. If ECM recognizes and indicates low MAP signal, ECM and 5-volt reference and MAP signal circuits are not at fault.

CODE 34, MAP SENSOR SIGNAL VOLTAGE LOW

Manifold Absolute Pressure (MAP) sensor responds to changes in manifold pressure (vacuum). If MAP sensor fails, ECM will substitute a fixed MAP value and use TPS input to control fuel delivery.

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

1. This confirms Code 34 and determines if code was a hard failure or an intermittent condition. Code 34 will set when ignition is on and MAP signal voltage is low. On some systems, engine must be running to set code.
2. Jumpering harness terminals "B" to "C" will determine if problem is sensor, ECM or wiring. If ECM recognizes and indicates high MAP signal, ECM and wiring are okay.
3. Scan tester may not display 12 volts. The important thing is that the ECM recognizes voltage as greater than 4 volts (high MAP voltage signal), indicating ECM and MAP signal circuit are not at fault.

CODE 34, MAF SENSOR SIGNAL VOLTAGE LOW 3.8L

Code 34 is set when engine is running without MAF sensor signal for greater than 4 seconds. If Code 34 is set, control module will substitute a value for MAF based upon RPM, TPS and IAC monitored parameters.

Note. Test numbers refer to numbers on diagnostic chart.

1. Determines if code is result of an intermittent or hard failure.
2. Voltage reading at sensor harness terminal "A" of less than 4 volts or more than 6 volts indicates fault in circuit No. 492 or poor connections.
3. Verifies both ignition voltage and a good ground are available.

CODE 36, SHIFT CONTROL PROBLEM (3.8L)

4T60E transaxle is electronically shifted. Within transaxle are 4 solenoids. Solenoid "A" is used for 1st and 4th gear operation only. Solenoid "B" is used for 1st and 2nd gear operation. Remaining 2 solenoids are for TCC operation only. All PRNDL indications are ignored as far as transaxle shifting is concerned except manual low. Code 36 will set if solenoid "B" failed in OFF position, which will cause transaxle to be in 4th gear, and desired gear is 1st, TPS is greater than 40 percent, engine speed is greater than 2000 RPM, VSS is 3-20 MPH and Codes 21, 22 and 24 are not present. Code will also set if solenoid "B" failed in ON position, which will cause transaxle to be in 1st gear, and desired gear is 4th, PRNDL is in 3rd or 4th, TPS is greater than 10 percent and Codes 31, 21 and 22 are not present. Code 36 does not turn on SERVICE ENGINE SOON light.

CODE 38, BRAKE SWITCH CIRCUIT (3.8L)

Code 38 will set if Code 24 is not present, status at brake input terminal of control module has not changed from high to low and vehicle speed has been greater than 35 MPH and back to zero MPH a precalibrated number of times.

Note. Test numbers refer to numbers on diagnostic chart.

1. Jumpering brake switch determines if ECM and wiring for brake switch are okay.
2. Determines if brake switch is out of adjustment or is faulty.
3. Verifies voltage to brake switch.

CODE 39, TCC CIRCUIT (3.8L)

Code 39 will set when TCC is commanded on, vehicle speed is greater than 35 MPH, throttle angle is greater than 10 percent, vehicle is in 3rd or 4th gear, Engine RPM-to-vehicle speed indicates TCC is not locked and all conditions have existed for more than 10 seconds. Code 39 does not turn on SERVICE ENGINE SOON light.

Note. Test numbers refer to numbers on diagnostic chart.

1. With ALDL test terminal grounded, PCM provides a ground for solenoid. This step tests for power to solenoid.
2. Tests to see if problem is faulty solenoid, power supply or driver circuit.
3. Tests TCC solenoid driver circuit at PCM.

CODE 41, CAM SENSOR CIRCUIT (3.8L)

Code 41 will set if engine is running and a cam sensor signal is not received by ECM for last 5 seconds.

Note. Test numbers refer to numbers on diagnostic chart.

1. Verifies proper operation of circuits No. 633, 644 and 645.
2. Tests circuit No. 630 from C(3)I module to ECM.
3. If camshaft gear magnet is interfacing with cam sensor, voltage reading will be zero. Bumping engine should correct this condition.
4. If voltage reading is constantly varying around a midpoint of 4.6 volts and connections are good, PCM is faulty.

CODE 42, ELECTRONIC SPARK TIMING (3.1L)

Code 42 indicates ECM has seen an open or short to ground in High Energy Ignition Electronic Spark Timing (HEI EST) system or by-pass circuits.

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

1. This test confirms Code 42 and determines if fault is a hard failure or intermittent condition.
2. This tests for a normal EST ground path through ignition module. If circuit No. 423 is shorted to ground, reading will be less than 500 ohms.
3. As test light voltage touches circuit No. 424, module should switch. This causes ohmmeter to "over-range" with meter in 100-200 ohm range. A higher ohm range will indicate over 5000 ohms. This test assures module switched.
4. If module did not switch, this step tests for a short in circuit No. 423, an open in circuit No. 424 and a faulty ignition module connection or module.
5. This step confirms Code 42 is a faulty ECM and not an intermittent problem in circuits No. 423 and 424.

CODE 42, ELECTRONIC SPARK TIMING (3.8L)

Code 42 will set if EST or by-pass circuit is open or grounded at time of engine start-up.

Note. Test numbers refer to numbers on diagnostic chart.

1. Tests if ECM recognizes a problem. If ECM does not set Code 42 at this point, problem is intermittent. Check for a loose connection.
2. With ECM disconnected, digital volt-ohmmeter should indicate less than 200 ohms. This is normal EST circuit resistance through ignition module. A higher resistance would indicate a fault in circuit No. 423, a poor ignition module connection or a faulty ignition module.
3. If test light was on when connected from 12 volts to ECM harness by-pass circuit, either circuit No. 424 is shorted to ground or ignition module is faulty.
4. Tests if ignition module switches when by-pass circuit is energizedby 12 volts through test light. If ignition module switches, resistance reading should switch from less than 200 ohms to more than 6000 ohms.
5. Disconnecting ignition module should make ohmmeter indicate as if it were monitoring an open circuit (infinite reading). Otherwise, circuitNo. 423 is shorted to ground.

CODE 43, ELECTRONIC SPARK CONTROL (3.1L)

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

1. If conditions for a Code 43 exist, scan tester will display YES. A knock signal should exist at idle unless an internal or system problem exists.
2. Determines if system is functioning. Usually, a knock signal can be made by tapping on exhaust manifold. If knock signal is not made, try tapping on engine block near sensor. On models with automatic transmission, it may be necessary to place gear selector lever in Drive.
3. Because Code 43 sets when signal voltage on spark retard line remains low, this test should cause signal on that line to go high. The 12-volt signal should be seen by ECM as a "no knock" signal if ECM and wiring are okay.
4. This test determines if knock signal is detected on sensor-to-controller line or if ESC module is at fault.
5. If sensor line is routed too close to secondary ignition wires, ESC module may see interference as a knock signal.
6. This checks ground circuit to module. An open ground will cause voltage on monitored line to remain constant at about 12 volts. This would cause Code 43 functional test to fail.
7. This should generate a knock signal to controller. This determines if ESC controller is operating correctly.

CODE 44, LEAN EXHAUST INDICATION

Sensor acts like an open sensor circuit and produces no voltage when exhaust temperature is less than 600°F (316°C). An open sensor circuit or cold sensor causes "open loop" operation.

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

1. Code 44 sets when O2 sensor signal remains low for a precalibrated period and system is operating in "closed loop".

O2 Sensor Wire

O2 sensor wire may be mispositioned and touching exhaust manifold. Check for ground between sensor and wire connector.

Fuel Contamination

Water, even small amounts, near in-tank fuel pump inlet can reach fuel injector, causing a lean exhaust and setting Code 44.

Fuel Pressure

System will be lean if fuel pressure is low. It may be necessary to monitor fuel pressure while driving vehicle. For fuel pressure checking procedure, see BASIC TESTING article in this section.

Exhaust Leaks

If exhaust system has large leaks, exhaust system negative pressure pulses can cause outside air to be drawn into system and past O2 sensor. Vacuum or crankcase leaks can also cause a lean condition. If Code 44 is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.

CODE 44 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

Scheme 118

CODE 45, RICH EXHAUST INDICATION

Sensor acts like an open sensor circuit and produces no voltage when exhaust temperature is less than 600°F (316°C). An open sensor circuit or cold sensor causes "open loop" operation. Code 45 indicates a rich exhaust and diagnosis should begin with: fuel pressure, leaking injector, HEI shielding, canister purge saturation, coolant sensor, MAP sensor, O2 sensor contamination and TPS intermittent output.

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

1. Tests if O2 sensor is registering a rich condition. Code 45 is set when vehicle is at operating temperature (in "closed loop"), throttle angle is greater than 5 percent, O2 sensor signal at ECM is greater than .75 volt for 60 seconds or more.

Fuel Pressure High

If fuel pressure is too high, air/fuel ratio will be rich. For fuel pressure checking procedure, see BASIC TESTING article in this section. The ECM can compensate for slight increases but if air/fuel ratio becomes too rich a Code 45 will be set.

Ignition Ground

If an open occurs at circuit No. 453, HEI induced electrical "noise" may result, causing simulated reference pulses picked up by ECM on EST harness reference line. Additional pulses result in a higher than actual engine speed signal. The ECM will increase injector pulse width ("on" time) to match increased RPM signal. Scan tester will show higher than actual RPM, which can help diagnose problem.

Fuel Canister

Charcoal canister fuel saturation will cause a rich air/fuel ratio. If full of fuel, check canister control and hoses.

MAP Sensor

If ECM senses higher than normal manifold pressure (low vacuum) system can go rich. Disconnecting MAP sensor allows ECM to substitute a fixed value for the MAP sensor. If rich condition disappears, replace MAP sensor and continue testing.

TPS

An intermittent TPS output will cause system to operate rich due to a false indication of engine acceleration.

O2 Sensor Contamination

O2 sensor contamination, caused by silicone in certain fuels or use of improper RTV sealant, may cause a White-powdery coating to cover O2 sensor. The false high signal voltage produced (or low oxygen content sensed) is interpreted by ECM as a rich mixture, causing ECM to set Code 45.

EGR Problem

EGR valve sticking open at idle is usually accompanied by a rough idle and/or stalling. If Code 45 is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.

CODE 45 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

Scheme 119

CODE 51, FAULTY PROM/MEM-CAL

Ensure all pins are fully inserted in socket. If okay, replace PROM/MEM-CAL, clear memory and recheck. If Code 51 reappears, replace ECM.

CODE 52, FAULTY CALPAK (EXCEPT 2.5L)

Ensure all pins are fully inserted in socket. If okay, replace CALPAK, clear memory and recheck. If Code 51 reappears, replace ECM.

CODE 55, ECM/PCM ERROR (EXCEPT 2.5L)

Ensure ECM grounds are good and MEM-CAL is properly latched. If okay, replace ECM/PCM. Clear codes and confirm closed loop operation. Check operation of SERVICE ENGINE SOON light.

CODE 54, FUEL PUMP CIRCUIT

Code 54 will set if ECM does not see 12 volts on fuel pump signal voltage monitor during the first 2 seconds after ignition is turned on.

Scheme 120

Scheme 121

CODE 56, QUAD-DRIVER "B" FAULT 3.8L (1 OF 2)

PCM uses Quad-Driver Modules (QDMs) to control several devices. When PCM is commanding a component on, voltage of output circuit will be low (near zero volts). When PCM is commanding component off, voltage of output circuit will be high (near battery voltage). Primary function of quad-driver module is to control ground circuit for component being controlled. PCM has an internal fault line for each quad-driver module. Fault line status can be displayed on a "Scan" tester. If PCM detects an output voltage other than what is expected on fault line, PCM will set Code 56.

Note. Test numbers refer to numbers on diagnostic chart.

1. PCM does not know which controlled circuit caused Code 56 to set. This chart will check each circuit to determine which is at fault. If other QDM-related codes are present, use those charts first.
2. If QDM "B" related symptoms are present, checks on Code 56 (2 of 2) chart should isolate cause of fault.
3. These steps help determine which circuit is out of specification.

CODE 56, QUAD-DRIVER "B" FAULT 3.8L (2 OF 2)

PCM uses Quad-Driver Modules (QDMs) to control several devices. When PCM is commanding a component on, voltage of output circuit will be low (near zero volts). When PCM is commanding component off, voltage of output circuit will be high (near battery voltage). Primary function of quad-driver module is to control ground circuit for component being controlled. PCM has an internal fault line for each quad-driver module. Fault line status can be displayed on a "Scan" tester. If PCM detects an output voltage other than what is expected on fault line, PCM will set Code 56.

Note. Test number refers to number on diagnostic chart.

1. 4) This step helps determine if problem is circuit or component.

Scheme 122

CODE 61, CRUISE VENT SOLENOID 3.8L

Cruise switch within turn signal lever receives ignition voltage from a 15-amp fuse on circuit No. 639. Cruise switches are inputs to cruise control portion of PCM. Cruise servo and vent and vacuum solenoids are output lines and are controlled by high side drivers in PCM. With ignition on, PCM looks at these output lines and will set a code depending upon actual status of these lines compared with commanded status. In this manner, PCM can detect opens or shorts to ground or voltage. Code 61 does not turn on SERVICE ENGINE SOON light.

Scheme 123

Scheme 124

CODE 62, CRUISE VACUUM SOLENOID 3.8L

Cruise switch within turn signal lever receives ignition voltage from a 15-amp fuse on circuit No. 639. Cruise switches are inputs to cruise control portion of PCM. Cruise servo, vent and vacuum solenoids are output lines and are controlled by high side drivers in PCM. With ignition on, PCM looks at these output lines and will set a code depending upon actual status of these lines compared with commanded status. In this manner, PCM can detect opens or shorts to ground or voltage. Code 62 does not turn on SERVICE ENGINE SOON light.

Scheme 125

CODE 63, CRUISE SYSTEM PROBLEM 3.8L

PCM monitors cruise control system servo position to ensure desired cruise position and actual cruise position are equal to each other. If servo position is low when maximum servo position is commanded, PCM will set Code 63. Code 63 does not turn on SERVICE ENGINE SOON light. If Code 61, 62 or 65 is set with Code 63, repair other code before using this flow chart.

Scheme 126

CODE 65, CRUISE SERVO POSITION 3.8L

PCM supplies 5 volts to cruise control servo position sensor. Depending upon actual servo position, voltage on servo position sensor circuit will indicate to PCM position of servo. Code 65 will set if circuit No. 399 is open or if circuit No. 398 is open or shorted to ground or voltage. Code 65 does not turn on SERVICE ENGINE SOON light.

Scheme 127

CODE 66, LOW A/C REFRIGERANT CHARGE 3.8L

PCM monitors A/C request and completes ground for A/C relay when an A/C mode is selected at control head and refrigerant pressure is sufficient to close pressure cycling switch. If A/C pressure is low and clutch cycles too often, PCM will protect compressor by disabling A/C relay and setting Code 66. Relay will be disabled until next ignition cycle. If Code 66 is set during 3 consecutive ignition cycles, A/C relay will be disabled until Code 66 is cleared from memory. Code 66 does not illuminate SERVICE ENGINE SOON light. Code 66 will set if A/C request signal lasts less than 1.5 seconds for 10 or more consecutive compressor "on" cycles within a 15 minute period.

Scheme 128

Scheme 129

CODE 67, CRUISE ENGAGE SWITCHES 3.8L

Code 67 will set if circuit No. 397 or 86 is open, set/coast or resume/accel switch is closed for an extended amount of time or any cruise engage switch circuit is shorted to voltage. Code 67 does not illuminate SERVICE ENGINE SOON light.

Scheme 130

Scheme 131

CODE 68, CRUISE SYSTEM PROBLEM USING TECH 1 (3.8L)

PCM-integrated cruise control system is designed to monitor itself to ensure desired cruise position and actual cruise position are equal to each other. Code 68 sets when actual servo position sensor signal is 15 percent greater than desired servo position sensor signal for .6 second. Code 68 does not illuminate SERVICE ENGINE SOON light. If Code 68 is current, vehicle will operate in "power management" mode. During this mode, PCM will shut of fuel to 3 cylinders to avoid overrevving engine in case of throttle being held open by cruise system malfunction. Power management mode may be perceived as a severe engine miss of lack of power.

Note. Test number refers to number on diagnostic chart.

1. Most VAC solenoids leak a small amount of vacuum when closed. However, they should not leak enough to allow WOT in 15 seconds with vent closed.
2. When VAC solenoid is forced on, vacuum will be vented to atmosphere unless vent valve is stuck closed.

CODE 69, A/C HEAD PRESSURE SWITCH 3.8L

A/C head pressure switch opens ground at 210 psi (14.77 kg/cm 2 ). When switch is open, fans should run at high speed. If Code 69 is set, engine cooling fans will run at high speed anytime A/C is requested.

Scheme 132

Scheme 133