Oxygen Sensor Fault, P0038 and P0157 fix - MechoMedics

Sunday, 27 May 2018

Oxygen Sensor Fault, P0038 and P0157 fix


Hello Readers, Technician, Mechanic and Diagnosticians. In a modern period when Diagnosis is gradually replacing 'Guess-Work' it won't be strange if you desire all vehicle warning light fixed and sorted; and even more than this, when fixes are fast, precise and services are comprehensive, you will definitely wanna get issues attended to by such a Diagnostician. Hence our service also includes diagnosis and fixing of foreign used Vehicles.
 We are on a quest to raise vehicle user's awareness on Warning Lights, Indicator and their Vehicle performance; and this has brought us in contact with several Vehicle Users, Dealers, Fleet Managers, Mechanics, Technicians, Engineers and even Readers like you. Warning lights come on when a fault is ongoing in any of the Vehicle Systems i.e.  Fuel and Air intake system, Exhaust Gas Recirculation System (EGR), Evaporative Emission (EVAP) System, Positive Crankcase Ventilation (PCV) System, Catalyst System, Transmission System and other Powertrain System; Antilock Brake System (ABS); Supplementary Restraint System (SRS), Airbag and Occupant Classification System; Instrument Cluster System; Heated Ventilation and Air Condition (HVAC) System; Intelligent Suspension System; Electric Parking Brake (EPB) System; Electronic Power Steering (EPS) System, e.t.c. Many  Systems, right? Yes, so many they are with more Sensors and Actuators and Modules that make each system able to detect ongoing faults. Detailed Diagnosis will help you to know what fault is ongoing and determine the best way of fixing such faults.

This fix can be credited to a Dealer friend who called us for Diagnosis on one of his newly acquired Vehicles, a 2007 Toyota Camry 3.5L V6 Engine that had the Diagnostic Trouble Code (DTC) as  P0038- Heated Oxygen Sensor Heater Control Circuit Bank 2 Sensor 2. Also a DTC P0157-  Oxygen Sensor Circuit Low Voltage Bank 2 Sensor 2 will also be mentioned in this article just to add more details to your fix.

Toyota Heated Oxygen Sensor and Air/Fuel Ratio Sensor are 2 sided Sensor with an Heater Circuit Side and a Sensor Circuit Side. Hence this single, solid piece sensor has a connector with 4 wires.

The Diagnosis for Heated Oxygen Sensor, Air/Fuel Ratio Sensor are similar and this involves the following;
1. Scanning of Powertrain System for DTC to know the location of the faulty sensor.
2. Testing of Sensor Heater Circuit:
 A. Continuity Test on the Sensor Heater Circuit (Same colored Wire) using a Digital Voltage and Ohms Meter (DVOM). No buzzing of DVOM signifies a dead Sensor.
 B. Resistance Test on the Sensor Heater Circuit (Same colored Wire) using a Digital Voltage and Ohms Meter (DVOM). This Sensors have various Resistance Value on their Heater Circuit at a given temperature. Hence precise test will involve you knowing the expected resistance of the sensor at the test temperature. Infinite resistance means a dead Sensor and the lower the resistance of the sensor to the specified value the better it is in performance.
3. Locate the Sensor Part Number using the Vehicle Identification Number (VIN).
The Sensor for this Vehicle reads TOYOTA 89465-06250 DENSO 1412
4. Loosen and Replace the Oxygen or A/F sensor using an SST or  a 22mm Open and Close End Spanner.

5. Clear the DTC and that is it.
We however go a step further by confirming the fix using our Diagnostic Tool to view a Live Data of the
Sensor Activity on Both Bank in the Upstream and Downstream Location. By revving the Engine, a similar quick response between the two similarly located Sensor at warm up and Closed Loop Fuel system status will mean a fix. Poor response on a sensor will generate the DTC P0157
after some Trips, this means that the Heater Circuit is fine but the Sensor Circuit is failing or failed.

 Slow response will also result from installing a wrong Sensor (With same appearance but different Resistance and Part Number allocation).

That's a fix guide you can employ. I hope you find this information useful as you carry out detailed Diagnosis and install the right Sensors.

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