Toyota Hilux 2008 2TR-FE – ECU swap


2TR-FE – TOYOTA HILUX 2008 – ECU SWAP, the long story

This vehicle came into the workshop with check engine light illuminated, with fault codes:

  1. P0037 – Oxygen Sensor Heater Control Circuit Low (Bank 1 Sensor 2)
  2. P2238 – Oxygen (A/F) Sensor Pumping Current Circuit / Open (Bank 1 Sensor 1)


The first thing we searched for was the location of the sensors and plugged in the scan tool to check the live data.
The live data of the A/F sensor did not move. The rear sensor o2 sensor measured 0.0v which was indicating a good fault! a visual inspection of the harness revealed that the rear 02 sensor plug had been melted from the exhaust and you could not disconnect the o2 sensor from the harness, Fault 1, rectify by 2nd hand 02 sensor and harness plug solder in place.rear-o2-sensor-burnt-harness

During visual inspection of the front A/F sensor it revealed there was a black wire into the A1A circuit which is the main sensing circuit of the A/F sensor the wire was live 12 volts all the time and was connected from ECU to the sensor, we decided to then pull out a wiring diagram and continue to resistance check the whole harness. We had repaired the harness to what we thought was right.
Reading the live data we could see that the A/F sensor only went to 1v. At first this was confusing then at a second thought could the 02 sensor have been the wrong part number? we got the second hand one with the same parts numbers, not thinking that the o2 Sensor that was installed in the vehicle was correct when the vehicle came in. Indeed the Sensor was wrong and searched for the correct part number and installed the correct sensor, Live data test again showed the sensor is now working, only to find that a new fault code had emerged.

DTC    P0031    Oxygen (A/F) Sensor Heater Control Circuit Low (Bank 1 Sensor 1)front-o2-sensor-wire-harness-cuts

How could this be we had resistance tested the whole harness, to find that the ECU was Indeed faulty, and no Ground circuits in the ECU was Allowing the heater actually function (the ecu controls the amount of  ON time for the heater with pulse width modulation) in the A/F Sensor which was where the fun begun to find the right part number for the Engine ECU, which brings us up to speed on the poor repairs and lack of understanding that other repairers will go to make the check engine light stay off.

Engine ECU programming is listed below (this is also listed so we don’t forget, ourselves, it is very hard to find this information in the workshop manual)

ECU Programming

  1. Install the new or second hand ECU
  2. bridge terminals 4 & 13 on OBD2 plug
  3. Turn ignition switch to ON.
  4. Wait 35 Mins.
  5. Switch Ignition OFF.
  6. Disconnect bridging Pin
  7. Start Vehicle.

 which left only the P0037 – Oxygen Sensor Heater Control Circuit Low (Bank 1 Sensor 2)

All that was left was the cut the harness and install new wiring to the heater circuit B+ and HT1B on terminal 2 of the ECU

Test drive the vehicle and all fixed,


After repairing the A/F Sensors wiring and then working out that ECU was not working for the heater chnage the ECU and Program. Finally the heater wiring repair for the Bank1 Sensor 2 (after Cat) Sensor, all is well that ends well.

Photos during the Repairs

Work flow sheet and resistance checks on all wiring for A/F sensors

Work flow sheet and resistance checks on all wiring for A/F sensors


TGN16R 2TR-FE, Engine Bay.


Found wire harness cuts to ECU for A/F Sensor to wrong places, repair to correct pin out

HA1A yellow Heater Ground Circuit broken in harness

HA1A yellow Heater Ground Circuit broken in harness

 Wiring Diagram for 2TR-fe Engine

PDF document download wiring-diagram-1tr-and-2tr