Fuel System > Engine Control System > P0037 HO2S Heater Control Circuit Low (Bank 1 / Sensor 2)

Component Location

General Description

The normal operating temperature of the HO2S(Heated Oxygen Sensor) ranges from 350 to 850°C(662 to 1562°F). The HO2S heater greatly decreases the amount of time required for fuel control to become active. The PCM provides a pulse width modulated control circuit to adjust current through the heater. When the HO2S is cold, the value of the resistance is low and the current in the circuit is high. On the contrary, if the temperature in the resistor of the sensor rises, the current drops gradually.

DTC Description

If the PCM detects short to ground or open in heater under detecting conditions, PCM sets P0037. MIL(Malfunction Indication Lamp) turns on when the malfunction lasts till consecutive 2 driving cycle.

DTC Detecting Condition

Item

Detecting Condition

Possible cause

DTC Strategy

•	Detects a short to ground or open

•	Poor Connection

•	Open in Power Circuit

•	Open or short to ground in control circuit

•	HO2S(B1/S2)

•

PCM

Enable Conditions

•	No disabling Faults Present

•	Engine Running

•	11V ≤ Ignition Voltage ≤ 16V

Threshold value

•	short to ground or open circuit

Diagnosis Time

•	Continuous (More than 5 seconds failure for every 10 seconds test )

MIL On Condition

•	2 Driving Cycles

Specification

Heater
Resistance (Ω)	8.1 ~ 11.1 Ω at 21 °C (69.8 °F)

Schematic Diagram

Signal Waveform And Data

Fig1) The signal waveforms of front HO2S(the upper) and heater(the lower) at idle

Fig2) The signal waveforms of rear HO2S(the upper) and heater(the lower) at idle

The HO2S requires a minimum temperature to provide a closed loop fuel control system. So the HO2S contains a heater element to reduce its warm-up time and ensure its performance during all driving conditions. The PCM controls this heater element by duty cycle. The main relay supplies voltage to the heater and the PCM provides a ground circuit for activating the heater.

Monitor DTC Status

Check DTC Status

(1)	Connect scantool to Data Link Connector(DLC).

(2)

IG "ON".

(3)	Select "DTC" button, and then Press "DTC Status" to check DTC's information from the DTCs menu.

(4)	Read "DTC Status" parameter.

(5)

Is parameter displayed "Present fault"?

	▶ Go to "Terminal and connector inspection" procedure.
	▶ Fault is intermittent caused by poor contact in the sensor's and/or PCM's connector or was repaired and PCM memory was not cleared. Thoroughly check connectors for looseness, poor connection, ending, corrosion, contamination, deterioration, or damage. Repair or replace as necessary and go to "Verification of Vehicle Repair" procedure.

Terminal And Connector Inspection

1.	Many malfunctions in the electrical system are caused by poor harness and terminal condition. Faults can also be caused by interference from other electrical systems, and mechanical or chemical damage.

2.	Thoroughly check connectors for looseness, poor connection, bending, corrosion, contamination, deterioration, or damage.

Has a problem been found?

	▶ Repair as necessary and go to "Verification of Vehicle Repair" procedure
	▶ Go to " Power Circuit Inspection " procedure

Power Circuit Inspection

■ Check Voltage

1.	IG "OFF" & Disconnect HO2S(B1/S2) connector.

2.	IG "ON" & ENG "OFF".

Measure voltage between power terminal of HO2S(B1/S2) heater harness connector and chassis ground.

Specification : B+

Is the measured voltage within specification ?

	▶ Go to "Control Circuit Inspection" procedure.
	▶ Repair open or short to ground in HO2S(B1/S2) Heater power circuit then, go to "Verification of Vehicle Repair" procedure.

Control Circuit Inspection

■ Check Short To Ground In Harness

1.	IG "OFF" and disconnect HO2S(B1/S2) connector.

Measure resistance between control terminal of HO2S(B1/S2) heater harness connector and chassis ground.

Specification : Infinite

Is the measured resistance within specification ?

	▶ Go to "Check Open in harness" as follows.
	▶ Repair short to ground in HO2S (B1/S2) heater control circuit and go to "Verification of Vehicle Repair" procedure.

■ Check open in harness

1.	IG "OFF" and disconnect HO2S(B1/S2) and PCM connector.

Measure resistance between control terminal of HO2S(B1/S2) heater harness connector and heater control terminal of PCM harness connector.

Specification : Approx. below 1Ω

Is the measured resistance within specification ?

	▶ Go to "Component Inspection" procedure.
	▶ Repair open in HO2S(B1/S2) heater control circuit and go to "Verification of Vehicle Repair" procedure.

Component Inspection

■ Check HO2S(B1/S2) Heater Resistance

1.	IG "OFF" and disconnect HO2S(B1/S2) connector.

Measure resistance between power and control terminals of HO2S(B1/S2) heater(Component Side).

Specification : 8.1 ~ 11.1 Ω at 21°C(69.8°F)

Is the measured resistance within specification ?

▶ Substitute with a known - good PCM and check for proper operation. If the problem is corrected, go to "Verification of Vehicle Repair" procedure.

There is a memory reset function on scantool that can erase optional parts automatically detected and memorized by PCM. Before or after testing PCM on the vehicle, use this function to reuse the PCM on the others.

▶ Substitute with a known - good HO2S(B1/S2) and check for proper operation. If the problem is corrected, go to "Verification of Vehicle Repair" procedure.

Verification Of Vehicle Repair

After a repair, it is essential to verify that the fault has been corrected.

1.	Connect scantool and select "DTC" button.

2.	Press "DTC Status" button and confirm that "DTC Readiness Flag" indicates "Completed". If not, drive the vehicle within conditions noted in the freeze frame data or enable conditions

3.	Read "DTC Status" parameter

Is parameter displayed "History(Not Present) fault"?

	▶ System performing to specification at this time. Clear the DTC
	▶ Go to the applicable troubleshooting procedure.