whats up guys, i have a obd2a p72 ecu i bought here on h-t, i just installed in on my car with a ex wiring harness that has a 5 wire primary o2, i have dtc 41 for primary oxygen sensor heater and assumed it was the o2 sensor so i didnt think much of it, but as i fault traced with the limited information i have i noted that the ecu should be sending batt voltage at pin a6 to the heater element on pos II and its duty cycle controlled after warm up, i checked the continuity from the wire at the ecm all the way to the sensor and its good, but im not getting 12 v on pos II, although i do have 12v at pin a5 which is the secondary o2 sensor heater element, the dtc check engine light turns on immediatly after the car is started, within 3 seconds, i reset the ecu, and i disconnected the ecu over night, still didnt go away, so im begging to think i was sold a bunk ecu since im not getting 12v only on pin a6 and only have a dtc for the primary sensors, or could this have somethign to do with the fact that its a 5 wire o2? which i highly doubt since the p72 uses a 4 wire so technically i should be able to ditch the wideband function of the o2. any ideas on this guys? please educated responses only, i do know what im doing just asking for confirmation, or if someone would be so kind, to check theyre pin a6 on theyre obd2a p72 ecu on pos II and see if they get 12v, if so, than its a bad ecu. THANKS GUYS!!! obd2a p72 ecu, 96-98 ex wiring harnass, 5 wire o2. dtc 41 primary o2 heater element, on at all times immediatly after startup solid dtc.

 

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by portfl0w &raquo;</TD></TR><TR><TD CLASS="quote">whats up guys, i have a obd2a p72 ecu i bought here on h-t, i just installed in on my car with a ex wiring harness that has a 5 wire primary o2, i have dtc 41 for primary oxygen sensor heater and assumed it was the o2 sensor so i didnt think much of it, but as i fault traced with the limited information i have i noted that the ecu should be sending batt voltage at pin a6 to the heater element on pos II and its duty cycle controlled after warm up, i checked the continuity from the wire at the ecm all the way to the sensor and its good, but im not getting 12 v on pos II, although i do have 12v at pin a5 which is the secondary o2 sensor heater element, the dtc check engine light turns on immediatly after the car is started, within 3 seconds, i reset the ecu, and i disconnected the ecu over night, still didnt go away, so im begging to think i was sold a bunk ecu since im not getting 12v only on pin a6 and only have a dtc for the primary sensors, or could this have somethign to do with the fact that its a 5 wire o2? which i highly doubt since the p72 uses a 4 wire so technically i should be able to ditch the wideband function of the o2. any ideas on this guys? please educated responses only, i do know what im doing just asking for confirmation, or if someone would be so kind, to check theyre pin a6 on theyre obd2a p72 ecu on pos II and see if they get 12v, if so, than its a bad ecu. THANKS GUYS!!! obd2a p72 ecu, 96-98 ex wiring harnass, 5 wire o2. dtc 41 primary o2 heater element, on at all times immediatly after startup solid dtc.</TD></TR></TABLE>

just curious, why are you using a 5 wire o2? does it indeed have the ability to read narrow band (0-1v)

i'd try yourself a 4 wire...i'd guess the 5 wire will not give you the narrow band function you need.

 

are you u sure u dont have a HX harness instead of a EX/y8 harness....the ex harness has a 4 wire o2 according to my wire harness....the hx came with the 5wire o2..

 

well, i bought the harness and teh guy said it was an ex, it has vtec on it, i dont see how using a 4 wire would fix the porblem if the ecu isnt putting out 12v thanks guys!

 

either way, if it isnt supposed to be a 5 wire, the ecm is still wired pin a6 heater power, and d7 signal output, with d11 being ground and g101 being groudn for the heater, so regardless it should still function as a regular o2 sensor, i woudl just be disabling the wideband portion, which works by the three wires in the middle, not connected im assuming, although i havent pinned them but its unneccesary.

 

these are the minimum amount of wires i should need connected in order to function as a 4 wire o2, which they are, i dont see how replacing the sensor could help. unless someone has tried this. this is based on the conclusion that a obd2a p72 uses a 4 wire o2

 

thinking about it, shoudl a ex harness already have a knock sensor installed on it? because i had to ad knock, so i believe its possible it wasnt a ex harness.n all in all i added iab, knock, swapped sensor connector for ckf, swapped connector for iat, and there is a loose connector 6 pin which does not connect to anything stemming off of the tps and map sensor wiring portion, thanks again guys!

 

when i pinned a6, i would get ground, when i would pin a5 i woudl get B+, this was strange to me almost hinting to a a/t type harness, which appears to be ground controlled by the ecm instead of B+ controlled, like i said i have minimal info meaning i have no diagrams and am just going off my knowledge which is not noob status... but than again a/t do not use 5 wire from what i understand based off of this diagram, confusing, why i assume i have a bad ecu.

 

bump for some help guys, i only ask when ive exhausted my attempts. followed proper fault tracing steps, just wanna confirm before i condemn the ecu

 

thanks for the tip on the hx, i didnt know this, so i went to a buddies house and looked at his haynes book and discovered that the p72 ecu controls the ground circuit on the heater element, not the power circuit as on the 5 wire, it would seem that i was sold a hx harness and told it was an ex, so in an attempt to get it to work, i jumped a 4 wire o2 sensor heater circuit to pin a6 (which gives ground to the circuit) i gave the sensor heater circuit B+ and connected the other end of the heater circuit from the o2 sensor straight to pin A6 , i figured this should work for sure, but, it didnt, although when i grounded it to pin A5 secondary o2 sensor heater control, it did ground and the sensor got hot. so. either there is something else in the harness which is not grounding the ecm correctly for only the A6 circuit, or i have a bad ecu still. does this seem right to you guys? btw i performed all my tests with teh primary o2 sensor unplugged, so it was an open circuit and the B+ i fed it only had one way to go, through the ecu. has aneyone had issues using an hx harness to install a b series with a p72 obd2a ecu? i even jumped pin A5 to pin A6 so they both got the same reference voltage supplied after the heating element on the secondary o2 sensor heater element. 12v, still got dtc 41. i think this ecu is not grounding pin a6....

 

You need a 4-wire O2 sensor, period. It almost reads like you're trying to use the 5-wire O2 sensor in some fashion that might 'mimic' the 4-wire output....which ain't gonna happen. If you've got the ability to plug a 5-wire wideband O2 into your engine harness, you do NOT have an Ex harness.

A P72 uses a 4-wire O2 sensor.

If anything, try to get a decently sized (wattage, that is) 15-40 ohm resistor and wire it to A6 and 12v. If you still get the CEL coming back on within 5 secs, then perhaps the ECU is dead. 15-40 ohms is the spec called out in the Helms manual.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by portfl0w &raquo;</TD></TR><TR><TD CLASS="quote">thinking about it, shoudl a ex harness already have a knock sensor installed on it? </TD></TR></TABLE>

yes.

 

ic, thanks, i didnt know that, i assumed the guy didnt lie and sold me an ex harness, like i said, i hooked up a known good 4 wire o2 sensor heater circuit to a6, and the o2 sensor i used had 12.8 ohms across the heater element, i gave it twelve volts. so than i guess i can call this ecu dead. i can convert this 5 wire into a 4 wire no problem. i just need to run power from the junction point to the black wire. or i can tap into the power feed for the secondary o2 sensor heating element since they both trace to the same junction box and they both feed off of a 7.5a fuse under the dash, as for the oxygen sensing portion of the sensor they white and green wire are wired the same so i should have no problems using that part on the sensor part itself. looks live ive been had! sold a bunk ecu and the wrong harnass... feel pretty stupid.

 

so yea, thanks for the help guys, im just gonna have to try a new ecu, ill wire the new sensor on soon, and buy a new ecu asap.

 

so yea, thanks for the help guys, im just gonna have to try a new ecu, ill wire the new sensor on soon, and buy a new ecu asap. ps. yea i realized i would not be able to use the 5 wire as a 4 wire when i got a hold of some schematics, i though the wideband portion was in addition to traditional o2 sensing, discovered the 5 wire has 2 heating elements and the wideband portion is the only way that it can read o2. thanks for the input guys appreciate it!!!

 

thanks alot ee_chris!!

 

update, removed the 5 wire o2, and wired up a known good 4 wire o2 in its place, i ran voltage to the heater element from the same location as the secondary heater element B+ so now im getting B+ at pin A5 and A6, now i just need a ecu

 

UPDATE== so after testing the ecu and coming to the conclusion that i have a bunk ecu, and thanks to vrd, the realization that i was sold a hx harnass instead of a ex harnass, i had to modify the hx harnass and get a new ecu, so it seems, ive been had TWICE! sold the wrong harnass! AND a bad ecu im gonna try to get the names of the guys, unfortunate because it was a while ago. i got a new ecu, and after wiring B+ to the o2 sensor heater instead of ground, i now have no dtcs, car runs the same, but no dtcs. so, what ive learned from this is to not buy shipped items, unless im positive of what they are. and will be able to verify they work promptly i also just bought a p/s pump from someone and there was some shipping issues, seller did not want to fix issues and now im stuck pumpless and down 25 bucks. looks like local pick ups for me from now on! glad i got rid of the dtc though! thanks alot for the positive input guys i appreciate it alot, special thanks to ee_chris .