Engine Controls - Tests W/codes - 3.1L: Diagnosis Oldsmobile Achieva I

SELF-DIAGNOSTIC SYSTEM

Note. Powertrain Control Module (PCM) is also be referred to as Electronic Control Module (ECM) in some diagnostic charts and figures. Terms are used interchangeably.

Control module is equipped with a self-diagnostic system, which detects system failures or abnormalities. When a malfunction occurs, control module will illuminate SERVICE ENGINE SOON light located on instrument panel. SERVICE ENGINE SOON light is also be referred to as the Malfunction Indicator Light (MIL). When malfunction is detected and light is turned on, a corresponding trouble code will be stored in control module memory. To retrieve stored codes, see RETRIEVING CODES (NON-SCAN) . Malfunctions are recorded as hard failures or as intermittent failures.

DIAGNOSTIC PROCEDURE

Diagnosis of computerized engine control system should be performed in following order

1. Ensure all engine systems not related to computer system are operating properly. DO NOT proceed with testing unless all other problems have been repaired. DIAGNOSTIC CIRCUIT CHECK must be performed before using trouble code charts. See «BASIC TESTING»(ref-19653) article in this section.
2. If trouble codes were displayed (other than Code 12), determine whether codes are hard or intermittent trouble codes. Hard codes will cause SERVICE ENGINE SOON light to glow continuously while engine is running. See «HARD OR INTERMITTENT TROUBLE CODE DETERMINATION»(ref-19583-S29740498902001031200000) . For diagnosing hard codes, proceed to appropriate trouble code chart. For diagnosing intermittent codes, proceed to INTERMITTENTS in «TESTS W/O CODES»(ref-19654) article in this section.
3. If no trouble codes are present and a driveability problem exists, refer to SYMPTOMS in «TESTS W/O CODES»(ref-19654) article in this section. Doing so will help identify proper system or component to check in «SYSTEM/COMPONENT TESTS - 3.1L»(ref-19615) article in this section.
4. After necessary repairs are made, clear trouble codes and perform FIELD SERVICE MODE CHECK in «BASIC TESTING»(ref-19653) article in this section.

Note. For information on retrieving codes using a scan tester, refer to user and reference manuals supplied with tester.

READING TROUBLE CODES

Control module stores component failure information under a related trouble code which can be recalled for diagnosis and repair. Trouble codes may be read by counting flashes of SERVICE ENGINE SOON light or by reading digital display on a scan tester. Scan tester is faster to use, more accurate and capable of reading information which otherwise would necessitate testing individual control module and sensor/solenoid connector terminals using a digital voltmeter. See SCAN TESTER USAGE and SCAN DATA .

Note. When using most scan testers, a time delay exists between serial data updates. For instantaneous response, a digital voltmeter must be used.

If scan tester is not available, reading flashes of SERVICE ENGINE SOON light is possible by grounding diagnostic test terminal "B" (if a wire is present) of DLC with ignition on and engine off. see scheme 1 For example, "FLASH, FLASH, pause, FLASH, longer pause" identifies Code 21. First series of flashes is first digit of trouble code. Second series of flashes is second digit of trouble code. Trouble codes are displayed starting with lowest numbered code. Each code is displayed 3 times. Codes will continue to repeat as long as DLC test terminal is grounded.

Note. Trouble codes will be recorded at various operating times. Some codes require operation of that sensor or switch for 5 seconds; others require operation for 5 minutes or longer at normal operating temperature, vehicle speed and load. Therefore, some codes may not set in a service bay operational mode and may require road testing vehicle in order to duplicate condition under which code will set.

TROUBLE CODE DEFINITION

ECM/PCM TROUBLE CODE DEFINITION

Note. Use trouble code charts only if SERVICE ENGINE SOON light is illuminated (indicating a current problem exists).

HARD OR INTERMITTENT TROUBLE CODE DETERMINATION

During any diagnostic procedure, determine if codes are hard failure codes or intermittent failure codes. Diagnostic charts will not usually help analyze intermittent codes. To determine hard codes and intermittent codes

1. Enter diagnostic mode. Read and record all stored trouble codes. Exit diagnostic mode, and clear trouble codes. See «CLEARING TROUBLE CODES»(ref-19583-S05436636342001031200000) .
2. Apply parking brake, and place transmission in Neutral or Park. Block drive wheels, and start engine. SERVICE ENGINE SOON light should go out. Run warm engine at specified curb idle for 2 minutes and note SERVICE ENGINE SOON light.
3. If SERVICE ENGINE SOON light comes on, enter diagnostic mode. Read and record trouble codes. This will reveal hard failure codes. Oxygen sensor related codes may require a road test to reset hard failure after trouble codes were cleared.
4. If SERVICE ENGINE SOON light does not come on, all stored trouble codes were intermittent failures, except as noted above.

CLEARING TROUBLE CODES

Note. On models not utilizing a 12-terminal DLC or if no wire is present in terminal "B", codes are cleared using a scan tester.

Turn ignition switch to ON position, and ground diagnostic test terminal "B" at DLC. see scheme 1 Turn ignition switch to OFF position, and remove control module fuse from fuse block for 10 seconds. Replace fuse. Remove diagnostic terminal ground lead. If fuse cannot be located, pigtail at battery can be disconnected. When power to ECM is remove, degraded driveability may be exhibited until control module "relearns" optimum operational parameters.

Diagnostic Aids

Diagnostic aids (located in many trouble code charts) are additional tips used to help diagnose trouble codes when inspected circuit is okay. Diagnostic aids may help lead to a definitive solution to trouble code problem.

SPECIAL TOOLS (DIAGNOSTIC)

Note. A scan tester plugged into DLC may be used to read trouble codes and check voltages in system on serial data line (terminal "E", or terminal "M"). This can save a great deal of time. For additional information, see SCAN TESTER USAGE and SCAN DATA .

Computerized engine control system is most easily diagnosed using scan tester; however, other tools may aid in diagnosing problems if a scan tester is unavailable. These tools are a tachometer, test light, ohmmeter, digital voltmeter with 10-megohm input impedance (minimum), vacuum pump, vacuum gauge, fuel injector test lights and 6 jumper wires 6" long (one wire with female connectors at both ends, one wire with male connectors at both ends and 4 wires with male and female connectors at opposite ends). A test light, rather than a voltmeter, must be used when indicated by a diagnostic chart.

Control module will not go into closed loop if code is set. Code may set if vehicle runs out of fuel or stalls while vehicle is in motion. If oxygen sensor ground becomes loose, a false oxygen sensor reading will occur. This can result in a Code 13 being set. On models equipped with an oxygen sensor heating element, element resistance should be 3.5-14 ohms.

CODE 13 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION

Code 13 Schematic (3.1L) Open Oxygen Sensor Circuit. Scheme 3

Code 13 Flow Chart (3.1L) Open Oxygen Sensor Circuit. Scheme 4

After engine is started, temperature should rise steadily to about 190°F (88°C) and then stabilize when thermostat opens. At normal operating temperature, signal voltage at control module terminal should be 1.5-2.0 volts. Check sensor for shifted calibration by using sensor TEMPERATURE-TO-RESISTANCE VALUES table. When code is set, control module will turn on electric cooling fan(s) if equipped.

CODE 14 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION

TEMPERATURE-TO-RESISTANCE VALUES (1)

Code 14 Schematic (3.1L) Coolant Temperature Sensor Signal Voltage Low. Scheme 5

Code 14 Flow Chart (3.1L) Coolant Temperature Sensor Signal Voltage Low. Scheme 6

After engine is started, temperature should rise steadily to about 190°F (88°C) and then stabilize when thermostat opens. At normal operating temperature, voltage at control module sensor signal line should be 1.5-2.0 volts. Check sensor for shifted calibration by using sensor TEMPERATURE-TO-RESISTANCE VALUES table. When code is set, control module will turn on electric cooling fan(s) if equipped.

CODE 15 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION

TEMPERATURE-TO-RESISTANCE VALUES (1)

Code 15 Flow Chart (3.1L) Coolant Temperature Sensor Signal Voltage High. Scheme 7

An intermittent cam reference signal can be caused by poor connection, cracked sensor or internal engine problems.

Code 17 Schematic (3.1L) Camshaft Sensor Error. Scheme 8

Code 17 Flow Chart (3.1L) Camshaft Sensor Error. Scheme 9

A scan tester displays throttle position in volts. Closed throttle voltage should be low. Voltage should increase gradually to about 4.5 volts at a steady rate as throttle angle is increased. If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.

CODE 21 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION

Code 21 Schematic (3.1L) Throttle Position Sensor Signal Voltage High. Scheme 10

Code 21 Flow Chart (3.1L) Throttle Position Sensor Signal Voltage High. Scheme 11

A scan tester displays throttle position in volts. Closed throttle voltage should be low. Voltage should increase gradually to about 4.5 volts at a steady rate as throttle angle is increased. If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.

CODE 22 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION

Code 22 Flow Chart (3.1L) Throttle Position Sensor Signal Voltage Low. Scheme 12

A faulty or misadjusted park/neutral switch may set a false Code 24. Use scan tester to check for proper signal in Drive while wiggling shifter. Code 24 may set if vehicle is power braked (brakes applied and throttle depressed) for more than 10 seconds.

Code 24 Schematic (3.1L) Vehicle Speed Sensor. Scheme 13

Code 24 Flow Chart (3.1L) Vehicle Speed Sensor. Scheme 14

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check for

1. Poor Connection Or Damaged Harness: Inspect PCM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.
2. Intermittent Test: Monitor Tech-1 while moving related connectors and wiring harness. If failure is induced, scan data will change from low to high, or high to low. This may assist in isolating the location of the malfunction.

Code 28 Schematic (3.1L) Transmission Range Pressure Switch. Scheme 15

Code 28 Flow Chart (3.1L) Transmission Range Pressure Switch. Scheme 16

With ignition switch in ON position and engine stopped, manifold pressure is equal to atmospheric pressure and signal voltage will be high. Comparison of BARO readings from a known good vehicle using same sensor is a good way to check accuracy of suspect sensor. Readings should be same within .4 volt. Code 33 will result if ground circuit is open, MAP signal circuit is shorted to voltage or to 5-volt reference circuit.

CODE 33 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION

Code 33 Schematic (3.1L) MAP Sensor Signal Voltage High. Scheme 17

Code 33 Flow Chart (3.1L) MAP Sensor Signal Voltage High. Scheme 18

A slow, unstable idle may be caused by a system problem which cannot be overcome by IAC. Scan counts will be greater than 60 if idle is too low and zero counts if idle is too high. If idle is too high, stop engine. Fully extend IAC with driver. Start engine. If idle speed is greater than 800 RPM, look for possible vacuum leaks.

An intermittent 24X signal and Code 36 can be caused by poor connections. Visually and physically check connections.

Code 36 Schematic (3.1L) 24X Signal Error. Scheme 19

Code 36 Flow Chart (3.1L) 24X Signal Error. Scheme 20

Code 37 can be caused by a misadjusted brake switch or a poor connection. Code may also be set by unusual driving habits i.e. stop-and-go expressway driving.

Code 37 Schematic (3.1L) TCC Brake Switch Error. Scheme 21

Code 37 Flow Chart (3.1L) TCC Brake Switch Error. Scheme 22

Scan tester does not have the ability to help diagnose Code

Code 41 Schematic (3.1L) Cylinder Select Error. Scheme 23

Code 41 Flow Chart (3.1L) Cylinder Select Error. Scheme 24

Code 41 Flow Chart. Scheme 25

Scan tester does not have ability to help diagnose a Code 42 problem. See INTERMITTENTS in TESTS W/O CODES article in this section.

Code 42 Flow Chart (3.1L) IC Circuit Open/Grounded. Scheme 26

Check knock sensor signal circuit for a potential open or short to ground. An open knock signal circuit would cause 5-volt reference to remain high at PCM knock signal terminal. A short to ground in knock signal circuit would cause 5-volt reference signal to pull low to near zero volts. Resistance to ground through knock sensor should be 3300-4500 ohms. Also check for proper installation of MEM-CAL.

Code 43 Schematic (3.1L) ESC Error. Scheme 27

Code 43 Flow Chart (3.1L) ESC Error. Scheme 28

Using scan tester, observe Block Learn Memory (BLM) value at different RPMs. If conditions for a Code 44 exist, block learn value will be about 150.

If other codes of lower number are set with Code 45, use those charts first. Malfunction in MAP or TPS sensor circuits can cause a Code 45 to set. If other codes are not set, Code 45, rich exhaust, is most likely caused by

Check harness routing for a potential short to ground in signal circuit. Temperature should rise steadily to approximately 85°C then stabilize. A skewed sensor could result in delayed shifts or TCC enabled complaints.

Use temperature-to-resistance table to check sensor at various levels to determine if sensor is out-of-calibration, which could result in firm shifts or TCC enable.

TEMPERATURE-TO-RESISTANCE VALUES (1)

Code 58 Schematic (3.1L) Transmission Temperature Sensor High Temperature. Scheme 29

Code 58 Flow Chart (3.1L) Transmission Temperature Sensor High Temperature. Scheme 30

Temperature should rise steadily to approximately 212 °F (90°C) then stabilize. A faulty connection or an open in ground or signal circuit can result in Code 59. A skewed sensor could result in firm shifts or TCC enabled complaints.

Use temperature-to-resistance table to check sensor at various levels to determine if sensor is out-of-calibration, which could result in firm shifts or TCC enable.

TEMPERATURE-TO-RESISTANCE VALUES (1)

Code 59 Flow Chart (3.1L) Transmission Temperature Sensor Low Temperature. Scheme 31

Code 59 Flow Chart. Scheme 32

Code 70 sets when signal voltage falls outside of the normal possible range of the sensor and is not due to a refrigerant system problem. If problem is intermittent, check for opens or short in the harness or poor connections.

Code 70 Schematic (3.1L) High A/C Pressure. Scheme 33

Code 70 Flow Chart (3.1L) High A/C Pressure. Scheme 34

Code 24 will set if vehicle speed is not detected at start off. Code 72 will set when vehicle speed has been detected and then lost.

Code 72 Flow Chart (3.1L) VSS. Scheme 35

An intermittent may be caused by a poor connection, chafed wire insulation, or a wire broken inside insulation. Intake plenum should be checked for possible plugged passages.

Codes 75/76/77 Schematic (3.1L) EGR Solenoid Error. Scheme 36

Codes 75/76/77 Flow Chart (3.1L) EGR Solenoid Error. Scheme 37

See Code 59 chart to check transmission temperature sensor temperature-to-resistance values. Also, check transmission fluid level.

Code 79 Schematic (3.1L) Transmission Fluid Overtemp. Scheme 38

Code 79 Flow Chart (3.1L) Transmission Fluid Overtemp. Scheme 39

Check all connections to transaxle pass-through connector. An open in the ignition feed circuit will cause multiple codes to set. If scan tester indicates TCC is working, road test vehicle. If engine RPM does not decrease when TCC engagement is indicated on TCC, diagnose transaxle for possible mechanical problem.

Code 80 Flow Chart (3.1L) Transaxle Component Slipping. Scheme 40

An open or shorted 3X signal will cause an "engine cranks but won't start" condition. An intermittent problem may set a Code 82.

Code 82 Schematic (3.1L) 3X Signal Error. Scheme 41

Code 82 Flow Chart (3.1L) 3X Signal Error. Scheme 42

If Code 86 is intermittent, all circuits leading to the PCM that are connected to the A/D multiplexer should be checked for an intermittent short to battery voltage. Monitor each input circuit on a scan tester and wiggle related circuits (wiring and connectors). Any circuit that intermittently shorts to battery voltage will show a change in data on the scan tester.

Code 86 Schematic (3.1L) Analog/Digital Error. Scheme 43

Code 86 Flow Chart (3.1L) Analog/Digital Error. Scheme 44

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.

Code 96 Schematic (3.1L) Transmission Voltage Low. Scheme 45

Code 96 Flow Chart (3.1L) Transmission Voltage Low. Scheme 46