DIY PGMFI Diagnostics - Code 41 PO2H

[ECU-MAN]

Disclaimer: The following is provided as a GUIDE ONLY, and neither myself nor Ozhonda take any responsibility for the outcomes of someone else doing the following. You follow these steps at your own risk!


No part of this DIY is to be reproduced with out acknowledgment of the site and author it came from, ie me and ozhonda.com. Do not rip parts off and claim them as your own.




PO2H "Primary Oxygen Sensor Heater". The PO2H is commonly located on the back of the dump pipe under the car between the cat and the sump. The PO2H helps heat up the Oxygen Sensor to operating temp at start up to get the O2 sensor working sooner. The Heater is a wire wound heater element.




Aim:

Diagnose code 41.





Required:

Basic Testing

- Digital Multi Meter
- paper clip




Symptoms

A faulty PO2H will trigger code 41. The Engine light will come on and code 41 will be registered in ECU memory. An open circuit in the PO2H is a common cause for code 41.




Basic Test


- Perform a Visual inspection and make sure the PO2H is connected.


PO2H Pin out Picture






wire side of connector back probing

HO2 wire colour

1 = wht
2 = grn or gry
3 = blk
4 = blk





**** Voltage Test ****




Set your multi meter to DC Volts ( 20v scale )




Step 1 ( Reference Voltage test )




Check the PO2H for its Reference Voltage from the ECU. Connect the Black Lead from your multi meter to the chassis for a good ground. Back probe* the PO2H with the Red lead to Pin 3 of the PO2H while the sensor is connected.

KOER* you must get 12v

If you get 12v proceed to step 2,

if you do not get 12v, repair open or short circuit to ECU from Pin 3 of PO2H to the below ECU Pin ( also see continuity test below )



OBDO = A15
OBDI = A25
OBDIIa = A11
OBDIIb = B1

If you do not get 12v from the ECU pin above, replace the ECU.





STEP 2




Check the PO2H Signal. Connect the Red Lead from your multi meter to the battery Positive terminal. Back probe* the PO2H with the black lead to Pin 4 of the PO2H while the sensor is connected.

KOER* you should get 12v.


also check the PO2H signal at the ECU end at the following pin bellow



OBDO = n/a
OBDI = A6; note 1994 - 1995 Accord A11
OBDIIa = A6
OBDIIb = C1



If You do not get 12v replace the ECU



***** Its is always best to check sensor outputs at the sensor side *****




**** Continuity Test ****




Set your multi meter to continuity. This setting is mostly a picture of a sound .))) when you touch the Red and Black leads together on your meter it should beep.


STEP 1

make sure the Ignition is off and unplug the PO2H Connector and the ECU Connectors for this test



Continuity test between PO2H Pin 3 and ECU, Connect your Red multi meter lead on the PO2H Pin 3, Back probe* the Black multi meter lead on the ECU Pin below that suits your car.




OBDO = n/a
OBDI = A25
OBDIIa = A11
OBDIIb = B1




your multi meter should beep and read short or 000.0ohms. Place the black multi meter lead on a good ground source. You should not get beeping; this is testing for short to ground.






STEP 2

make sure the Ignition is off and unplug the PO2H Connector and the ECU Connectors for this test




Continuity test between PO2H Pin 4 and ECU, Connect your Red multi meter lead on the PO2H Pin 4, Back probe* the Black multi meter lead on the ECU Pin below that suits your car.




OBDO = n/a
OBDI = A6; note 1994 - 1995 Accord A11
OBDIIa = A6
OBDIIb = C1



your multi meter should beep and read short or 000.0ohms. Place the black multi meter lead on a good ground source. You should not get beeping, this is testing for short to ground.


If any of your continuity tests fail between the PO2H and ECU, repair the OPEN in the wire between the PO2H and ECU that failed.

If any of your continuity tests fail between the PO2H and ground, Find the short circuit and repair it. look for squashed wires, or for damage to any part of the PGMFI loom.









**** Resistance Test **** Set the multi meter to ohms ( 1K scale )




Unplug the PO2H, connect your Red multi meter lead to Pin 3 of the PO2H. Connect your Black multi meter lead to Pin 4 of the PO2H.



the resistance should be between 10 to 40 ohms



reset the ECU and road test the car.






* Notes

KOEO = Key On Engine Off

KOER = Key On Engine Running

Back probe the sensor, use a paperclip and push it into the connector then touch/clip your multi meter lead to the paper clip




Disclaimer: The following is provided as a GUIDE ONLY, and neither myself nor Ozhonda take any responsibility for the outcomes of someone else doing the following. You follow these steps at your own risk!

[barefootbonzai]

good shit right der.

[dAzLr]

so where do pins 1 and 2 go too on obdiia ecu ?

[ECU-MAN]

pin 2 goes to D7 and pin 1 goes to ground

[VTec1987]

pin 2 goes to D7 and pin 1 goes to ground

i thought d7 connect to pin 1 and pin 2 is grounded

[marcoardeno]

is this code causing limp mode or not? mine atm throwing code 41, idle seems hunting within 300rpm range (eg. 800-1100rpm) thanks

[ECU-MAN]

although the engine light comes on, you should be able to get your full RPM range ( even VTEC ) dont think limp is enabled with P02H

[marcoardeno]

yeah its confirmed not in limp mode because vtec kicks in. but however is it normal that the idle seems hunting a little bit because of code 41? thanks

[ECU-MAN]

I would not expect to have idle problems with the engine light on with out limp mode.

[ECU-MAN]

the O2 sensor is working. the ECU does know what your mixtures are ( when the engine is warm ).

your O2 heater that heats the sensor so it works quicker that is faulty.

if the O2 was faulty then you would get code 1.

fix you O2 heater then see if you have idle problems. then fix your idle problems

[ECU-MAN]

you cant fix the heater, you have to replace the O2

call your local honda dealer with your VIN handy and they can quote you.

[marcoardeno]

how about aftermarket o2 sensor like bosch in terms of quality and durability? oem o2 sensor costs so much!