DTC P0134 O2S Circuit Insufficient Activity Sensor 1. Chevrolet Cavalier (CNG) 2000

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 2000 🢒 Cavalier (CNG) 🢒 Engine 🢒 Engine Controls - 2.2L 🢒 DTC P0134 O2S Circuit Insufficient Activity Sensor 1

Engine Controls Components
Engine Controls Schematics
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The Oxygen Sensor (O2S) is used in order to determine the oxygen content of the engine's exhaust. The oxygen content of the exhaust indicates when the engine is operating lean or rich. When the engine is operating lean the exhaust will have more oxygen content. Once at operating temperature, the O2S will produce a voltage in relation to the oxygen content of the exhaust. The O2S requires an operating temperature of 360°C (600°F) to produce voltage. The O2S will produce more voltage when the exhaust is rich and less voltage when the exhaust is lean. The O2S operating voltage range is around 0.10 volts (100 mV) to 1 volt (1000 mV).

The gasoline control module (VCM/PCM or ECM) supplies a bias (or reference) voltage to the O2S. This bias voltage is around 450 millivolts. The AF ECU monitors the bias voltage as well as the voltage produced by the O2S.

During normal Closed Loop fuel control operation the AF ECU will add fuel (enriches the mixture) when the O2S indicates a lean exhaust content. When the O2S indicates a rich exhaust content the AF ECU will subtract fuel (leans-out the mixture). This oscillation above and below the bias voltage (sometimes referred to as activity or switching) can be monitored with the O2S signal voltage.

This DTC is used to indicate an O2S with in-active signal voltage.

Conditions for Running the DTC

•	The engine is operating on alternative fuel.

•	Engine speed is greater than 500 RPM.

•	The engine has been operating for at least 2 minutes.

•

The AF ECU determines the O2S has been at operating temperature for at least 2 minutes. The engine coolant temperature must be greater than 40°C (104°F) AND the calculated mass air flow must be above 6 grams per second for 2 minutes in order for the AF ECU to determine the O2S is at operating temperature.

Conditions for Setting the DTC

The AF ECU monitors an O2S signal voltage stuck between 0.347 V and 0.550 V (in-active) for 9 seconds continuously.

The AF ECU monitors an O2S signal voltage between 0.00 V and 1.0 V that has not performed a Rich/Lean switch for 15 seconds continuously.

Action Taken When the DTC Sets

The AF ECU will operate in Open Loop fuel control.

•	A first failure of this DTC will NOT illuminate the MIL and will store as Last Test Failed but not as History.

•	The AF ECU will illuminate the MIL and store the DTC as History after TWO consecutive drive trips that the diagnostic runs and fails.

•	The AF ECU will record operating conditions at the time the DTC sets. This information will be stored as Freeze Frame data.

Conditions for Clearing the MIL/DTC

•	The Last Test Failed status will clear when the DTC runs and passes.

•	The AF ECU will turn OFF the MIL after 3 consecutive drive trips that the DTC runs and passes.

•	The History status will clear after 40 consecutive WARM-UP cycles with NO failures of ANY DTC.

•	All DTC Information can be cleared using a scan tool.

•	Interruption of Control Module (AF ECU / VCM / PCM or ECM) power or ground MAY clear DTC Information. Clearing DTC Information with this method is inconsistent and should not be performed.

Diagnostic Aids

Fault Not Present

Fault Not Present indicates the condition that caused the DTC to set is intermittent and not currently present. Refer to Intermittent Conditions Symptom diagnosis for additional information. If any additional DTCs were stored proceed to the applicable DTC table in the order stated in the OBD System Check.

Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

This step determines if proper sensor activity is present. When in Closed Loop fuel control the O2S voltage should rapidly swing above and below the bias voltage.

This step determines if the gasoline control module and the High and Low circuits between the control module and the O2S connector are operating properly.

Step

Action

Value(s)

Yes

Did you perform the AF Powertrain On-Board Diagnostic (OBD) System Check?

Go to Step 2

Go to Alternative Fuels (AF) Powertrain On Board (OBD) System Check

Using a scan tool establish communication with the AF ECU.
Capture the DTC Information from the AF ECU into the scan tool.
Clear the DTC Information using a scan tool.
Reset the Fuel Trim values.
Start and idle the engine until normal operating temperature is reached.
Using a scan tool monitor the O2S voltage for the sensor that applies to this DTC.

Is the O2S voltage fixed within the voltage range specified?

0.00 to 1.0 V

Go to Step 5

Go to Step 3

The condition that set this DTC is not present. This DTC may have been set by one of the following conditions:

•	O2S connector water intrusion

•	An intermittently open O2S High signal circuit

•	An intermittently open O2S Low circuit

•	An O2S Low circuit with high resistance to ground

•	AF ECU ground circuits with high resistance to ground

•	Poor O2S or control module connector terminal contact

•	An exhaust system leak (typically within 12 inches up-stream of the O2S)

•	A defective O2S

Repair any of the above conditions as necessary.

Was a condition found and repaired?

Go to Step 16

Go to Step 4

The fault is not present. Refer to Diagnostic Aids.

Are any DTC's stored that have not been diagnosed?

Go to Diagnostic Trouble Code (DTC) List

Go to Intermittent Conditions

Using a scan tool establish communication with the GASOLINE control module (VCM/PCM or ECM).
Start and idle the engine until normal operating temperature is reached.
Using a scan tool monitor the O2S voltage for the sensor that applies to this DTC.

Is the O2S voltage fixed within the voltage range specified?

0.00 to 1.0 V

Go to Step 6

Go to Step 11

Turn the ignition OFF.
Disconnect the O2S connector for the sensor that applies to this DTC.
Jumper the O2S High signal circuit to a known good ground.
Turn the ignition ON leaving the engine OFF.
Using a scan tool monitor the O2S voltage for the sensor that applies to this DTC.

Is the O2S voltage LESS than the value specified?

20 mV

Go to Step 10

Go to Step 7

Turn the ignition OFF.
Remove the jumper from the O2S terminal.
Disconnect the gasoline control module (VCM/PCM or ECM) connector containing the O2S High and Low circuits.
Using the J 39200 DMM measure the resistance of the O2S High signal circuit between the control module connector terminal and the O2S connector terminal (engine harness side).
Measure the resistance of the O2S Low circuit between the Low circuit terminal and a PCM ground circuit terminal at the PCM connector.

Is the individual resistance of both circuits less than the value specified?

5 ohms

Go to Step 8

Go to Step 9

Inspect for proper gasoline control module (VCM/PCM or ECM) connector terminal contact.
Repair terminals as necessary.

Was a terminal repair made?

Go to Step 16

Go to Step 15

Repair the circuit that measured high resistance.

Is the action complete?

Go to Step 16

Inspect for exhaust system leaks upstream of the suspect O2S.

The leak may be very small and will typically be within 12 inches of the suspect O2S.

Repair exhaust as necessary.

Was an exhaust system repair made?

Go to Step 16

Go to Step 13

Inspect the oxygen sensor signal and low circuit for continuity between the AF ECU connector terminals and the oxygen sensor connector terminals.
Inspect these circuits for shorts to other circuits or to ground.

Ensure the oxygen sensor, gasoline control module and the AF ECU connectors are disconnected before testing circuits.

Repair wiring as necessary.

Was a wire repair made?

Go to Step 16

Go to Step 12

Replace the AF ECU. Refer to Engine Control Unit Replacement .
Program (flash) the replacement control module with the correct vehicle software and calibration.

Is the replacement complete?

Go to Step 16

Perform the AF Fuel System diagnosis and return to this step. Refer to Fuel System Diagnosis .

Was a CNG fuel system problem found and repaired?

Go to Step 16

Go to Step 14

Replace the O2S sensor. Refer to Oxygen Sensor Replacement in the Engine Controls section of the gasoline service manual.

Is the replacement complete?

Go to Step 16

Important: The following control module replacement procedures must all be completed before attempting to operate the vehicle.

Replace the gasoline control module (VCM/PCM or ECM). Refer to Powertrain Control Module Replacement .
Program (flash) the replacement control module with the correct vehicle software and calibration.

Important: In order to perform the variation learn procedure a switch-over to gasoline operation is necessary. Remove the CNG 20 amp fuse in order to perform the switch-over.

Perform the Crankshaft Position System Variation Learn in the Engine Controls section.

All of the above procedures are located in the gasoline service manual.

Is the replacement complete?

Go to Step 16

Reconnect all disconnected or removed components, connectors, fuses, etc.
Using a scan tool clear all DTC Information from BOTH the gasoline control module (VCM/PCM or ECM) and the AF ECU.
Using the scan tool communicate with BOTH the gasoline control module and the AF ECU in order to reset the Fuel Trim values to zero.
Start the engine.
Operate the vehicle within the Conditions for Running this DTC until the scan tool indicates the diagnostic ran.

Does the scan tool indicate the DTC passed?

System OK

Go to Step 2