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Y7/y8 in ex coupe, been dealing with heater element malfunction codes and it’s driving me nuts. I freeze frame scanned and they are working properly and getting proper fluctuating voltage. I checked the harness under intake, fuses 15 is fine, and the o2s show resistance on the plug. The car runs rich as hell and back fires slightly sometimes. It has a full header back and new cat, not oem. Anyone know what could be causing this ****?
Y7 block/Y8 head? Where are the two O2 sensors located?
Turn the key from OFF to ON(II) (don't start the engine).
Does the charging system warning light in the cluster turn on and stay on?
yes y7 non vtec block, y8 head. Model ex trim so everything else is vtec including p2p ecu. The o2s are located near exhaust manifold coming off engine bay harness ”upstream”, and downstream is post cat.
When the key is in the on position; the battery light is on, and the check engine light is solid, one quick flash, then solid.
yes y7 non vtec block, y8 head. Model ex trim so everything else is vtec including p2p ecu. The o2s are located near exhaust manifold coming off engine bay harness ”upstream”, and downstream is post cat.
When the key is in the on position; the battery light is on, and the check engine light is solid, one quick flash, then solid.
Sounds like the O2 sensor heaters are not properly wired to the ECU and fuse 15. Did you verify that each O2 sensor connector gets battery voltage from fuse 15?
Sounds like the O2 sensor heaters are not properly wired to the ECU and fuse 15. Did you verify that each O2 sensor connector gets battery voltage from fuse 15?
Yes I’ve tested both harness side and 02 side. And live scanned while driving, they get proper voltage. And fuse 15 is not blown.
The next step is to verify proper wiring of the heater ground wires to the ECU by performing continuity tests with a multimeter.
What year Civic EX?
P2P ECU?
1998 civic EX, p2p ecu. There is no continuity, I’ve come to the conclusion that it’s the ecu since the CEL is consistently solid, the o2s are new, and their is no open short in the wiring.
Describe specific electrical tests that led to this^ conclusion.
I’ve tested multiple times but I will do a conclusion test tomorrow and post results. But I am certain the primary oxygen sensor harness side plug has voltage, the o2 heater element black wires show resistance on both o2s. The a6 pin I believe shows voltage(correct if I’m wrong on pin), fuse 15 has 10-12 volts with key II ON. Only reason I have not changed ecu is because car runs fine beside being rich
I’ve tested multiple times but I will do a conclusion test tomorrow and post results. But I am certain the primary oxygen sensor harness side plug has voltage, the o2 heater element black wires show resistance on both o2s. The a6 pin I believe shows voltage(correct if I’m wrong on pin), fuse 15 has 10-12 volts with key II ON. Only reason I have not changed ecu is because car runs fine beside being rich
In each O2 sensor connector, one heater pin receives voltage from fuse 15 and another pin supplies ground to the heater voltage via ECU pin A6 (primary) or ECU pin A5 (secondary). See the two diagrams below.
Use an end-to-end continuity test to determine whether the heater ground wires properly run to ECU pin A5 or A6.
In each O2 sensor connector, one heater pin receives voltage from fuse 15 and another pin supplies ground to the heater voltage via ECU pin A6 (primary) or ECU pin A5 (secondary). See the two diagrams below.
Use an end-to-end continuity test to determine whether the heater grounds wires properly run to ECU pin A5 or A6.
thank you loads for the diagrams, really appreciate the help man. Couldn’t I test continuity through the prongs on the plug through pin a5 and a6? How should I go about it?
thank you loads for the diagrams, really appreciate the help man. Couldn’t I test continuity through the prongs on the plug through pin a5 and a6?
Yes. Touch or clip one multimeter probe to pin A5 or A6 in unplugged ECU connector A and the other meter probe to the Blk/Wht wire pin in one of the unplugged O2 sensor connectors.
Yes. Touch or clip one multimeter probe to pin A5 or A6 in unplugged ECU connector A and the other meter probe to the Blk/Wht wire pin in one of the unplugged O2 sensor connectors.
okay I will post results tomorrow thank you very much keep posted
Yes. Touch or clip one multimeter probe to pin A5 or A6 in unplugged ECU connector A and the other meter probe to the Blk/Wht wire pin in one of the unplugged O2 sensor connectors.
I disconnected SECONDARY oxygen sensor, probed pin 3 and Body ground, got good voltage and no continuity. Pin 4 got no voltage and showed continuity with body ground. Same for primary oxygen sensor. Between pin a5, pin 3/4, and body ground there was no continuity. I replaced fuse 15 with a known good 7.5, took the ground off the battery and reset the ecu. Upon starting it, the CEL light stayed off way longer than usual, about a minute. Then popped on. I repeated the process of taking the ground off and resetting the ecu, the code popped on immediately. What now?
I disconnected SECONDARY oxygen sensor, probed pin 3 and Body ground, got good voltage and no continuity. Pin 4 got no voltage and showed continuity with body ground. Same for primary oxygen sensor. Between pin a5, pin 3/4, and body ground there was no continuity. I replaced fuse 15 with a known good 7.5, took the ground off the battery and reset the ecu. Upon starting it, the CEL light stayed off way longer than usual, about a minute. Then popped on. I repeated the process of taking the ground off and resetting the ecu, the code popped on immediately. What now?
I disconnected SECONDARY oxygen sensor, probed pin 3 and Body ground, got good voltage and no continuity. Pin 4 got no voltage and showed continuity with body ground. Same for primary oxygen sensor. Between pin a5, pin 3/4, and body ground there was no continuity.
See diagrams
Secondary O2 sensor - On the wire harness side, pin 4 but not pin 3 should have battery voltage with the key in ON(II). Pin 3 but not pin 4 should have continuity with ECU pin A5.
One possibility is that you were actually testing the primary O2 sensor connector, suggesting that the two O2 sensors may be connected to the wrong connectors.
What wire colors did you test at pins 3 and 4 and ECU pin A5? Posting pics of the O2 sensor and ECU connector pins and wires may help.
Last edited by muellersfan; Jan 10, 2020 at 06:53 PM.
Secondary O2 sensor - On the wire harness side, pin 4 but not pin 3 should have battery voltage with the key in ON(II). Pin 3 but not pin 4 should have continuity with ECU pin A5.
One possibility is that you were actually testing the primary O2 sensor connector, suggesting that the two O2 sensors may be connected to the wrong connectors.
What wire colors did you test at pins 3 and 4 and ECU pin A5? Posting pics of the O2 sensor and ECU connector pins and wires may help.
Ended up borrowing a scanner and freeze framed a live data feed. I have no long term fuel trim meaning I’m in open loop, my Secondary o2 sensor is getting 1.070 volts instead of a up and down constant. Do you see anything else I’m missing that’s wrong with my sensors ? My EVAP Monitors are not ready also
D16y8 head, y7 block in 1998 civic ex. full header back brand new o2 sensors and cat. I have 2 CEL codes for p0135 and p0141, heater elements. There is no shorts in the wiring harness, fuse 15 is fine. I freeze frame scanned while driving but don’t know the specifics of what my map, IAT, etc should be. Can any one help me out? Anyone ever experience this
The ECU probably won't compute fuel trim unless it is confident the primary O2 sensor is OK (no sensor codes). So you need to resolve the P0135 first.
Make sure your new sensors are properly pinned. The heater wires (usually black, though sometimes they are white, but they are always the two wires on the sensor that are the same color) need to go to the black/yellow and black/white wires in the harness.
Disconnect the battery and unplug the ECU-- everything else still plugged in normally. Check that the sensor drive wires (A5 and A6) are not shorted to ground. There will be some resistance but if it is near zero track down the short. Then measure resistance from one of the fuse 15 black/yellow wires under the hood to the sensor drive wire at the ECU plug. This should be the same resistance you measured at the sensor, I think that 10 to 40 ohms is OK. Then reconnect the battery (ECU still unplugged), turn the key on and confirm that voltage appears at A5 and A6 at the ECU plug.
If all of this checks out, the ECU is probably bad.
Yesimchill I have merged all your threads into one. Please refrain from creating multiple identicle threads about the same issue and the same car!
Keep all your posts about this car in this thread, the consequences otherwise will likely be not being able to get information from this site for a duration.
Thank you.
Last edited by TomCat39; Jan 22, 2020 at 05:39 AM.
P0135 P0141!!
