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Discussion Starter #1 (Edited)
Hello Everyone,

Air/Fuel Ratio Relay*


I have a 05 rsx type s with cel P0135 that doesn't want to leave! I've replaced my primary upstream O2 sensor with denso 234-9064. After replacing the O2 sensor the cel was still there. I made sure I took the terminals out for more than 30 mins. After reading many forums I end up using the multimeter to find out I'm not getting any current in the clip shown in the picture. Before I pull any of those wires out to check from that clip I also read somewhere Air/Fuel sensor relay could be the solution. Now I've looked everywhere in the owner's manual to find this A/F relay and can't find it. I did check the A/F fuse 2 and 14 to make sure they weren't bad. I know the sensor is good but there is something wrong with either the relay or the wiring itself. I have attached a picture of the wiring and everything seems intact. Any help would be appreciated at this point.

Thanks in advance
 

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Not too sure if the '05 position is the same as the earlier models, but the AF sensor relay is in a cluster of 4 other relays under the glove box to the left of the ECM on the earlier years. There's an illustration on pg 22-9 of the Helm.
 

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Discussion Starter #3
Not too sure if the '05 position is the same as the earlier models, but the AF sensor relay is in a cluster of 4 other relays under the glove box to the left of the ECM on the earlier years. There's an illustration on pg 22-9 of the Helm.
Thanks I'll check it out as soon as I get home from work. Hopefully replacing this solves the problem. So I checked these 4 terminals again and I was getting 2.5v in one and 1.5v in the other, where as I checked my other car's terminal I got 12v using the multimeter. Any thoughts? I'm not getting sufficient voltage to the cables would this be caused by a bad relay? Thanks
 

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It could be a bad relay, but it could be a lot of other things also. First, have you reset the ECU by pulling fuse #6 in the under-hood fuse box? Sometimes the ECU will latch a code even though you've cleared the problem.

If you've reset the ECU and still have the code, you could try swapping the sensor heater relay with another similar relay to see if the problem follows. P0135 indicates a short or open on the heater circuit. The idea of the heater circuit is to get the sensor heated quickly with battery voltage and the voltage is switched on/off by the relay. So battery voltage may or may not be at the heater depending on how hot the sensor is. I haven't got good schematics of the circuit, so I can't help you much in running down the wires.
 

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Discussion Starter #5 (Edited)
It could be a bad relay, but it could be a lot of other things also. First, have you reset the ECU by pulling fuse #6 in the under-hood fuse box? Sometimes the ECU will latch a code even though you've cleared the problem.

If you've reset the ECU and still have the code, you could try swapping the sensor heater relay with another similar relay to see if the problem follows. P0135 indicates a short or open on the heater circuit. The idea of the heater circuit is to get the sensor heated quickly with battery voltage and the voltage is switched on/off by the relay. So battery voltage may or may not be at the heater depending on how hot the sensor is. I haven't got good schematics of the circuit, so I can't help you much in running down the wires.
Jay Thank you for all your help so far, so I called 2 Acura dealership (parts/service) and they had no idea about A/F ratio sensor relay lol They said there is no such thing so I came home and looked in the shop manual as you described. After finding it I was able to pull the sensor out but unfortunately I wasn't able to swap to test relay since this one is different then the rest. Should I order this relay online or just buy it from the dealership or is there a way to test a relay? For anyone who wants to know the part number is 7001 5316 by MITSUBA. I will include the pictures so everyone can have an idea how PIA it is just to replace their A/F ratio sensor relay on their rsx. I will replace this unless I can find a way to test it. Hopefully this solves my problem if not I'll be back :) Thanks once again and enjoy the pics!
 

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You can test the relay. There should be four contacts. Two of them will go to the coil and the other two are the switch contacts that connect +battery to the heater. I think the switch contacts should be normally open. Use alligator clip jumpers to jump battery voltage to the coil contacts ( a 9v battery may work). You should hear a click as the normally open contacts close. You should be able to see 0 ohms when the switch contacts close and infinite ohms when they open again as you remove voltage.

I see $25 or more for the relay OEM relay. I think I'd go to an auto parts store and spend $10 for one with the same contacts in the same positions on the relay, but test the original one first. I don't see any specs for the Mitsuba.
 

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Discussion Starter #10
You can test the relay. There should be four contacts. Two of them will go to the coil and the other two are the switch contacts that connect +battery to the heater. I think the switch contacts should be normally open. Use alligator clip jumpers to jump battery voltage to the coil contacts ( a 9v battery may work). You should hear a click as the normally open contacts close. You should be able to see 0 ohms when the switch contacts close and infinite ohms when they open again as you remove voltage.

I see $25 or more for the relay OEM relay. I think I'd go to an auto parts store and spend $10 for one with the same contacts in the same positions on the relay, but test the original one first. I don't see any specs for the Mitsuba.
Thanks I will try and see.
 

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After replacing 3 new O2 sensors and I kept getting the cel P0135 I was able to locate the problem. The problem was the Air/Fuel ratio sensor relay that's behind the glove compartment. I have provided the pictures above. Thanks Jay for helping me locate that relay since the dealership (service) didn't even know that relay exist for O2 sensor. I was able to save a lot of $$ :) THANKS!
 

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hate to revive an old thread, but im curious (since I also have this code) - did you use the above steps to check your old relay, or did you just put in a new one and see if the problem would go away?
 

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hate to revive an old thread, but im curious (since I also have this code) - did you use the above steps to check your old relay, or did you just put in a new one and see if the problem would go away?
I did test the relay after spending so much time figuring everything else out. This was my last go to. Only if this damn relay was in a better place it would have been my first few steps to check rather than changing 3 different O2 sensors. The Acura dealer didn't even know about this relay, they kept telling me to change O2 sensor and check fuse. The relay was only $7 at Auto Zone and it works fabulous.
 

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How did you go about testing the relay? I tried checking the service manual for some resistances and such but the procedure for diagnosing this CEL code is basically check everything else and replace the relay if everything else is fine (similar to what You did haha). Any pointers on which of the 4 pins i should check for what kind of resistance? If I had a brand new one that I could compare it with that might be the best way to figure it out.
 

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You can test the relay. There should be four contacts. Two of them will go to the coil and the other two are the switch contacts that connect +battery to the heater. I think the switch contacts should be normally open. Use alligator clip jumpers to jump battery voltage to the coil contacts ( a 9v battery may work). You should hear a click as the normally open contacts close. You should be able to see 0 ohms when the switch contacts close and infinite ohms when they open again as you remove voltage.
:iamwiths: you can use any 9-12v battery to test it. also theres usually a diagram on the side of the relays(dont know about oems) that shows you which contacts go to the coil.

good luck
 

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How did you go about testing the relay? I tried checking the service manual for some resistances and such but the procedure for diagnosing this CEL code is basically check everything else and replace the relay if everything else is fine (similar to what You did haha). Any pointers on which of the 4 pins i should check for what kind of resistance? If I had a brand new one that I could compare it with that might be the best way to figure it out.
Post #9 spells out the procedure.
 

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So the relay does not have any markings on it to indicate which two terminals correspond to the coil - a quick search on the internet gave me some helpful info. The two pins that have a resistance (mine showed around 100ohms, and on my mitsuba rc-5001 relay it was the silver pins - the other two are copper colored) are the pins for the coil - I wired up a 9V battery to these pins and heard it click (it works). Time to keep digging -_-
 

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Just because it clicks doesn't mean its working. You have to measure continuity in the other two pins. Should change from zero to infinity (if normally closed) when the coil is activated, or the other way around if normally open.
 

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I realized that after I wrote the post, but I checked it while it was still out. The resistance went between zero and infinity, so the relay is in fact good :thumbsup: thanks for the comment though!
 

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I did test the relay after spending so much time figuring everything else out. This was my last go to. Only if this damn relay was in a better place it would have been my first few steps to check rather than changing 3 different O2 sensors. The Acura dealer didn't even know about this relay, they kept telling me to change O2 sensor and check fuse. The relay was only $7 at Auto Zone and it works fabulous.
bumping a dead thread for info

how did you go about finding it at auto zone? is it a universal relay? will probably just replace mine and hope it works as I suck at using a multimeter lol
 
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