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Old 11-19-2017, 04:10 PM   #1
2006Impreza2.5i
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Default Dash and Headlights flicker, CEM not picking up reading from O2 sensor

I've got a 2006 2.5i.
My O2 sensor hasn't been working for a while now, and I put a new sensor in so I guess I've got a problem with the wiring or ECM. I also have noticed that my dash display and headlights have a consistent flicker that is basically non-stop. Do the lights flickering mean that my alternator is going out, or could this all be coming from an open/short circuit or bad ECM?
Here's some other info that might be helpful in finding out what might be the issue:
  • recently changed accessory belts myself, maybe I put them on too loose/tight? (I tightened to 1/4 inch flexion under "moderate finger pressure")
    -for a couple days after I changed the belts, I noticed a "deep whining"? sound (I assume from the power steering pump) when I'd turn the wheel at really slow speeds, like turning out of a parking spot. I haven't noticed that sound in the last couple weeks though
  • I have an after market stereo that was put on by the previous owner, wiring must be loose or something because sometimes it disconnects for a second if I bump it. The input also changes when I turn the headlights on/off
I appreciate any advice or ideas on what could be my problem, I want to look into as much by myself as possible before I go burn some cash on having someone else look into it
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Old 11-21-2017, 03:15 PM   #2
2006Impreza2.5i
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Brake Light just came on today. I changed my fluid two days ago and the fluid level is fine.
So Iím thinking it must be a grounding issue?
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Old 11-21-2017, 04:01 PM   #3
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Verify that your belt isn't slipping.
Put a voltmeter across the battery with the engine running, make sure the voltage is stable and in the 14V range with the engine at operating temperature. You can do a crude check for AC ripple by switching your meter to AC volts and taking a reading. It should be very low, no more than a few millivolts. Ideally the proper way to check for AC (which means bad diodes in the alternator) is with a scope.
Test the battery or have a parts store test it, this is usually free.
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Old 11-22-2017, 10:27 AM   #4
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Quote:
Originally Posted by Mulder View Post
Verify that your belt isn't slipping.
Put a voltmeter across the battery with the engine running, make sure the voltage is stable and in the 14V range with the engine at operating temperature. You can do a crude check for AC ripple by switching your meter to AC volts and taking a reading. It should be very low, no more than a few millivolts. Ideally the proper way to check for AC (which means bad diodes in the alternator) is with a scope.
Test the battery or have a parts store test it, this is usually free.
Agreed.
Voltage may only be 13.5 volts at idle, should be around 14.4 volts at high idle.

Check engine to chassis grounds as they have rotted off by now. I believe yours are from under the heads near the front to the chassis, one on each side.
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Old 11-22-2017, 08:57 PM   #5
2006Impreza2.5i
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Thanks for the replyís!
I had Autozone do a test on the battery last night and their tester said I need a new battery, but Iím still holding a charge. I believe itís coming time for a new battery anyway.
Iíll do those tests with my multimeter tonight.
Also, my brake light came on because I guess I didnít tighten one of my bleed screws all the way and I was leaking brake fluid... hehe. I bled the brake again to make sure there was no air in the line, refilled the fluid and tightened the screw for good.
While at work I did a hard battery reset and when I was driving home, my car about died on me... It was after I had driven 20ish miles and at first the radio and dash flicked off and on, 30 seconds later it happened again, then when I was going up a hill the car about completely died. Thankfully it didnít! I was able to make it home after taking it real easy up the hill (I live less than a mile away at that point). When I pulled in the driveway I turned the car off, and I was able to start it up again right away.
Iím thinkin this means itís definitely the alternator, right?
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Old 11-22-2017, 11:35 PM   #6
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It means nothing, check the voltages at the battery at idle and high idle. A poor battery can overwork the alternator, so you really have no clue at this point.
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Old 11-23-2017, 12:35 AM   #7
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Quote:
Originally Posted by Charlie-III View Post
It means nothing, check the voltages at the battery at idle and high idle. A poor battery can overwork the alternator, so you really have no clue at this point.
My engine idle fluctuates between 500-1000 by itself.
The voltages on my battery during idle fluctuates between 14.60-14.70 without accessories. With accessories, the voltages are all over the place... spiking at 15, dropping to 13.5ish when the ac fan kicks on, and it fluctuates around 14.75.
When I turned the car off the battery started at 12.84 and is slowly dropping.
Thanks for the help man!
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Old 11-23-2017, 12:17 PM   #8
Charlie-III
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Sound so it sounds like the alternator is charging, but you also need to check AC voltage ripple as Mulder suggested. The alternator may still have an issue as well as a failing battery.

The battery test done is likely looking at voltage drop with a load, the capacity has dropped below a percentage saying the capacity is down either due to dryout or plate sulfation.
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Old 11-23-2017, 02:14 PM   #9
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The 15V readings are a bit concerning depending on whether that's with the engine warmed up and what the ambient temp is. The only time I'd expect to see the system charging close to 15V is on a cold engine in the winter, and it should drop down to 14ish once it warms up as the regulator is thermally compensated.
Also the jumping around isn't good. The system should charge at a stable voltage, when a load is added there may be a brief dip before the alternator takes up the load and the voltage returns to where it was. If the total load is sufficient to exceed the charging capability of the alternator then the voltage will decrease but it still shouldn't jump around. This typically will happen only at idle as that's where the alternator output is lowest, and I'm not sure how likely it is on your '06 (it depends on the alternator rating). I know it does happen on my '02 with the 75A alternator.
As Charlie suggested you want to check the condition of all the main grounds as well as power cables, this includes the battery clamps and post connections. The clamps should be tight on the posts and there should be no corrosion between the clamp and post, and the cable-to-clamp connection should also be sound with no corrosion apparent. Replace any clamps or cables that look questionable.
Your voltmeter can be used to check for voltage drops between the battery positive and alternator power connection as well as between the battery negative and engine/chassis grounds. These checks should be done with some loads turned on so there is a significant current draw. Any positive-to-positive or negative-to-negative drop that exceeds a few tenths of a volt should be investigated as it indicates a possible cable or connection issue.
Going back to your O2 sensor issue, that may be a totally separate thing or it could be related. One possibility if the car sits outside is that mice or other critters have been chewing on the wiring which can cause all sorts of strange electrical symptoms. If you can get under the car, examine as much of the O2 harness as possible for signs of damage.
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Old 11-27-2017, 02:12 AM   #10
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Alright, so I didn't drive at all during Thanksgiving weekend. But I took my car around the block for a little test drive, it accelerated just fine without any accessories on. However, when I put on the AC, interior lights, and head/fog lights then accelerated I got it to stall/die a couple times. The engine didn't die until I came to a complete stop, but it would start right back up?
When I got back, I took readings on my battery with my DMM and I had a 14.65ish voltage with no accessories (no fluctuation this time?). Then when I'd take a reading with loads, the reading would drop to 12.7ish and fluctuate to 11.8-12.8 when the fan would kick on.
I checked AC ripple on my +/+ and I only got a reading of 0.005V and my -/- ripple was just 0.010-0.060V on my grounds (the only grounds I could find were the two adjacent to each other on the front of the engine behind the belts, the one on the engine by the trans oil dipstick, and the one right by the battery on the body). These readings didn't change much at all with loads on. All my battery and ground connections look fine and are good and tight.

Any thoughts on what could be causing the engine to stall/lose power? Just a reminder that I have a couple CEL codes: P0131 (ECM is not receiving a reading from S1B1 O2 sensor) and P0442 (small EVAP leak, I've had this code before but I got a new gas cap and it kept the code away for a while, I guess that wasn't the only issue...). I also think I have faulty piston rings or valve cover gaskets because I burn oil (that I top off regularly).
I'm thinking it has to be electrical because the lights cut out without the engine losing power sometimes with full loads on while accelerating.
I'm gonna be taking my car into a mechanic that a family member knows on Tuesday to see if he's got a possible solution.
Thanks for all your guys' help, again
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Old 11-28-2017, 01:48 PM   #11
Charlie-III
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Ignition (spark) is dependent on voltage to the coils. If the plugs are old as well as the coils and poor connections (grounds, power feeds, etc.), you need more power.
The voltage into the coils, or the grounds out may drop spark voltage enough at low revs to kill spark.

AC voltage ripple should be across the battery posts engine running or alternator out to ground.

DC Voltage from alternator out to battery positive, or battery negative to engine/ground is voltage drop through the cable.

The first is checking the diodes in the alternator (AC measurement) the second is loose through a high load cable.
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Old 12-06-2017, 12:22 AM   #12
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A P0131 means you have a short/open in your wiring to your 02 sensor, improper air/fuel ratio, a failed heater circuit portion of the 02 sensor or a bad ecu. Since your experiencing engine operation issues and you've already replaced the sensor, then that likely rules out a failed sensor or its heater circuit. The primary 02 sensor is important to the ecu for fuel trim. Check the harness out. If it is damaged it can cause damage to the ecu and the sensor as well, it sounds like that might be the case with how your engine is running but it seems like it is suffering mainly from an improper air/fuel ratio. Try driving the car on a cold start, before it warms up. This will keep the engine running in open loop (without the use of the 02 sensor for fuel trim), if it still runs poorly then it's likely your ecu but look at the wiring for the 02 sensor carefully, as I said it can cause damage to the next ecu you put in. The other thing that makes me think it's your ecu is if for whatever reason it is bad it could be damaged in such a way that it's electronic load circuit and alternator control circuit are now faulty as well, making it seem like you have a bad alternator. The flickering dash lights could also be the sub par wiring job by the radio installer. The dash lights are controlled by an illumination control module and one of it's circuits is the radio's illumination. The stereo has an illumination sensing wire on it so that it will dim and match your cluster and switches. If that wire is shorting to power or ground then it could be the cause and/or it could have damaged the illumination control unit. I would at least pull the radio and double check all the wiring.

Last edited by IanT-EJ22; 12-06-2017 at 12:58 AM.
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