DTC P0146 HO2S Circuit Insufficient Activity Bank 1 Sensor 3. Cadillac Concours 1997

For 1990-2009 cars
Engine Controls Components
Heated Oxygen Sensors
OBD II Symbol Description Notice
ESD Notice

### Circuit Description

The PCM provides a 0.45 volt reference to the oxygen sensor on CKT 1668. When the Oxygen Sensor reaches operating temperature it will generate a counter voltage that will vary based on the amount of oxygen in the exhaust. The post-converter heated oxygen sensor is located in the exhaust after the catalytic converter. A lean exhaust will generate a low voltage and cause the 0.45 reference to move lower. A rich exhaust will generate a high voltage and cause the 0.45 reference to move higher. If the oxygen sensor cannot respond under the test conditions and generate a voltage greater than 0.609 volt or less than 0.307 volt, it will set a DTC P0146. Possible causes of DTC P0146 are:

• | Open in CKT 1668 or 1669.

• | Short to voltage on CKT 1668 or 1669.

• | Oxygen sensor that malfunctions.

• | An ineffective oxygen sensor heater.

• | A poor HO2S ground.

### Conditions for Setting the DTC

#### Test Conditions

• | DTCs P0117, P0118, P0122 and P0123 not set.

• | Coolant temperature 75°C (167°F) or greater.

• | Throttle between 2.2 and 81.6 degrees.

• | (Calculated) Throttle position switch open.

• | Engine speed between 800 and 3000 RPM.

#### Failure Condition

Oxygen sensor voltage stays between 0.307 volt and 0.609 volt for 250 out of 300 seconds, oxygen sensor voltage not toggling.

### Action Taken When the DTC Sets

• | The PCM will illuminate the Malfunction Indicator Lamp (MIL) after two consecutive drive trips that the diagnostic runs and fails.

• | The PCM will record operating conditions at the time the DTC sets. This information will be stored in the Freeze Frame and Failure Records.

• | A first failure of this DTC will store in Last Test Failed but not History.

### Conditions for Clearing the MIL/DTC

• | The PCM will illuminate the Malfunction Indicator Lamp (MIL) after two consecutive drive trips that the diagnostic runs and fails.

• | The PCM will record operating conditions at the time the DTC sets. This information will be stored in the Freeze Frame and Failure Records.

• | A first failure of this DTC will store in Last Test Failed but not History.

### Diagnostic Aids

Notice: Do not solder heated oxygen sensor wires. Soldering the wires will result in the loss of the air reference to the sensor. Refer to Engine Electrical for proper wire and connection repair techniques.

A loose HO2S or one with a poor exhaust ground may cause this DTC to set. Before replacing an HO2S always check the resistance of the sensor ground. On a COLD engine, measure the resistance between the HO2S low circuit and the PCM ground at the PCM connector. If the resistance measures more than 500 ohms (typically less than 50 ohms), remove the sensor and check for corrosion at the HO2S sensor threads. Clean the HO2S sensor threads, apply a coating of anti-seize compound (5613695 or equivalent) and torque the HO2S sensor to the proper torque. Recheck HO2S ground resistance and replace any sensor with resistance above 500 ohms.

### Test Description

Number(s) below refer to the step number(s) on the Diagnostic Table.

1. Voltage on the scan tool should fluctuate above 0.6 volt and below 0.3 volt. If voltage remains above 0.6 volt, check the Post HO2S High circuit for a short to voltage. If voltage remains below 0.3 volt, check the Post HO2S High circuit for a short to ground.

2. Measuring voltage with a voltmeter will isolate a sensor problem from a PCM wiring problem.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | Go to A Powertrain On Board Diagnostic (OBD) System Check

2

1. Start the engine and warm-up until engine coolant temperature is the same or more than the value specified.
2. Connect the scan tool.
3. View Bnk. 1 Sns. 3 oxygen sensor reading for 30 seconds.

Does voltage remain between the specified values?

85°C (185°F)

0.3 - 0.6 volts

Go to Step 3

Fault not present

3

1. Turn the key to OFF.
2. Disconnect post-converter heated oxygen sensor connector.
3. Start the engine.
4. Using DMM J 39200 measure voltage between pins A and B (sensor side).

Does voltage remain between the specified values?

0.3 - 0.6 volts

Go to Step 6

Go to Step 4

4

1. Record the fluid life indexes, turn the key to OFF and wait 30 seconds.
2. Disconnect PCM connector C1.
3. Measure the resistance between PCM connector C1 terminal 47 and oxygen sensor connector terminal B.

Is the resistance the same or less than the value specified?

5 ohms

Go to Step 5

Go to Step 8

5 | Measure the resistance between PCM connector C1 terminal 48 and oxygen sensor connector terminal A. Is the resistance the same or less than the value specified? | 5 ohms | Go to Step 13 | Go to Step 9

6

1. Turn the key ON, engine OFF.
2. Measure the voltage between oxygen sensor terminals C and D (harness side).

Is the voltage the same or more than the value specified?

10.5 volts

Go to Step 12

Go to Step 7

7 | Measure the voltage from terminal D (harness side) to ground. Is the voltage the same or higher than the value specified? | 10.5 volts | Go to Step 10 | Go to Step 11
8 | Repair the open in the Post HO2S High circuit. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --
9 | Repair the open in the Post HO2S Low circuit. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --
10 | Repair the open in the Post HO2S ground circuit. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --
11 | Repair the open or short to ground (blown fuse) in the Post HO2S Ignition feed circuit. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --
12 | Replace the post-converter heated oxygen sensor. Refer to Heated Oxygen Sensor (HO2S) Replacement (Pre- and Post-Converter) . Is the replacement complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --

13

1. Check terminal contact at the PCM connector C1 terminals 47 and 48.
2. Repair terminal contact if needed.

Was terminal contact repaired?

--

Go to Powertrain Control Module Diagnosis for Verify Repair

Go to Step 14

14 | Replace the PCM. Refer to PCM Replacement/Programming . Is the replacement complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --