Engine Controls - Tests W/codes: Diagnosis Geo Metro I

DIAGNOSTIC CODE CHARTS

Note. Following diagnostic flow charts and mini-schematics are courtesy of General Motors Corp.

DIAGNOSTIC CIRCUIT CHECK

Diagnostic circuit check is an organized approach in identifying a problem created by an electronic engine system malfunction. It must be the starting point for any driveability complaint diagnosis, because it directs the service technician to the next logical step in diagnosing a complaint. Understanding the chart and using it correctly will reduce diagnostic time and prevent unnecessary replacement of good parts.

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

1. Checks Malfunction Indicator Light (MIL) operation.
2. Checks if ECM's self-diagnostic mode is operating.
3. Checks if ECM's serial data output is operating.
4. Checks if engine will start. If engine will not start, go to CHART A-3 in BASIC TESTING article in this section.
5. Checks for any codes that are stored in ECM memory with engine running.
6. Checks for any codes that are stored in ECM memory with engine off.
7. Compares ECM's control data to typical data values.
8. Checks if code(s) are intermittent problems.

Diagnostic Circuit Check Schematic. Scheme 13

Diagnostic Circuit Check Flow Chart. Scheme 14

Diagnostic Aids

Check connectors for contamination, corrosion or for bent

terminals.

Chart A-1 Flow Chart No Malfunction Indicator Light (MIL). Scheme 15

Normal O2 sensor voltage will vary from 0-.9 volt. Code 13 will be set if voltage is low or high all the time. A loose or intermittent O2 sensor ground can set a Code 13. O2 sensor ground is located on lower right rear of intake manifold.

After engine is started, temperature should rise steadily to about 203°F (95°C) and stabilize when thermostat opens.

Codes 14, 23 and 32 set at the same time could be a result of an open in Light Green/Black sensor ground wire.

When replacing ECT sensor, check TEMPERATURE TO RESISTANCE VALUES table. A "shifted" sensor could result in driveability complaints.

Code 14 Schematic ECT Sensor Circuit, Low Temperature Indicated. Scheme 16

Code 14 Flow Chart ECT Sensor Circuit, Low Temperature Indicated. Scheme 17

After engine is started, temperature should rise steadily to about 203°F (95°C) and stabilize when thermostat opens.

Ensure engine is not overheating and has not been subjected to conditions which would create an overheating condition (i.e., overload, trailer towing, heavy stop and go traffic, etc.).

When replacing ECT sensor, check TEMPERATURE TO RESISTANCE VALUES table. A "shifted" sensor could result in poor driveability complaints.

Code 15 Flow Chart ECT Sensor Circuit, High Temperature Indicated. Scheme 18

See ADJUSTMENTS article in this section for TP sensor adjustment. Codes 21 and 22 set at the same time could be the result of an open Light Green wire between ECM and TP sensor.

Code 21 Schematic Throttle Position Sensor CKT, Signal Voltage High. Scheme 19

See ADJUSTMENTS article in this section article for TP sensor adjustment. Codes 21 and 22 set at the same time could be the result of an open Light Green wire between ECM and TP sensor.

Code 22 Flow Chart Throttle Position Sensor CKT, Signal Voltage Low. Scheme 20

When replacing IAT sensor, refer to TEMPERATURE TO RESISTANCE VALUES table. A "shifted" sensor could result in poor driveability complaints.

Code 23 Schematic Intake Air Temperature Sensor CKT, Low Temperature Indicated. Scheme 21

Code 23 Flow Chart Intake Air Temperature Sensor CKT, Low Temperature Indicated. Scheme 22

If speedometer cable is binding, Code 24 can be set. Ensure that speedometer cable is free from restrictions and has a secure connection to instrument cluster. If problem is intermittent, refer to TESTS W/O CODES article in this section.

Code 24 Schematic Vehicle Speed Sensor Circuit. Scheme 23

Code 24 Flow Chart Vehicle Speed Sensor Circuit. Scheme 24

When replacing IAT sensor, refer to TEMPERATURE TO RESISTANCE VALUES table to evaluate possibility of a "shifted" sensor. A "shifted" sensor could result in poor driveability complaints. For IAT sensor specification, refer to I - SYS/COMP TESTS article in this section.

Code 25 Flow Chart Intake Air Temperature Circuit, High Temperature Indicated. Scheme 25

Check for blocked or pinched vacuum hose to MAP sensor. An intermittent condition may be caused by rubbed-through insulation, or a broken wire inside insulation. Check ECM harness connectors for backed-out or damaged terminals.

Code 31 Schematic MAP Sensor Circuit, Low Voltage Input - Low Vacuum. Scheme 26

Code 31 Flow Chart MAP Sensor Circuit, Low Voltage Input - Low Vacuum. Scheme 27

Check for leaking vacuum hose to MAP sensor. An intermittent condition may be caused by rubbed-through insulation, or a wire broken inside insulation. Check ECM harness connectors for backed-out or damaged terminals.

Code 32 Flow Chart MAP Sensor Circuit, High Voltage Input - High Vacuum. Scheme 28

An intermittent condition may be caused by rubbed-through insulation, or a wire broken inside insulation. Check ECM harness connectors for backed-out or damaged terminals. If code is intermittent, refer to TESTS W/O CODES article in this section.

Code 41 Schematic Ignition Signal Circuit, No Signal. Scheme 29

Code 41 Flow Chart Ignition Signal Circuit, No Signal. Scheme 30

A loose or damaged CMP sensor could cause an intermittent code. A misaligned CMP sensor or improper air gap could also set a Code 42. If code is intermittent, refer to TESTS W/O CODES article in this section. For CMP sensor specifications, refer to I - SYS/COMP TESTS article in this section.

Code 42 Schematic Camshaft Position Circuit, No Signal For 2 Seconds. Scheme 31

Code 42 Flow Chart Camshaft Position Circuit, No Signal For 2 Seconds. Scheme 32

An intermittent condition may be caused by poor or loose connection at ECM. This could cause a code to be falsely set.

Check all throttle body vacuum hoses and EGR valve. Check MAP sensor vacuum hose for leaks or restrictions. ECM will periodically turn off the EGR VSV when EGR is enabled in closed loop operation. Code 51 will set if corresponding manifold pressure change is less than a calibrated value, determining that a fault exists in the EGR system.

Code 51 Schematic Exhaust Gas Recirculation Circuit. Scheme 33

Code 51 Flow Chart Exhaust Gas Recirculation Circuit. Scheme 34