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Discussion Starter · #1 ·
Hey there.. First post here but I could really use some help. About 24 hours after Head Gaskets were done (2007 Outback 2.5i 140k miles on car) I get an AT Oil Temp light flashing. Relatively convinced it wasn’t overheating (it was -2 F) I drove home and did some research. Looks like it could be electrical mishap during head gasket work. Someone on CarGurus was saying to someone with roughly the same problem that it could be a grounding wire. And actually my passenger side grounding wire has been 100% severed for months and the other side is in relatively rough shape.

So I took it out later that afternoon to see if the lights would come on again and sure enough about 200 yards from home it popped on as well as the AWD light flashing too.
Can anyone help me out here? I’m about to take it back into the shop tomorrow (and I do trust them) but I really don’t want to have to keep going back and forth fishing for the source.
 

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It could be anything related to the transmission or ABS system, (since the AWD light is on). Is the ABS lit up? You would need to retrieve codes from the modules in order to ascertain where to go next. The TCM will flash the light for TCC, AT Temp sensor, incorrect gear ratio, and a few more.

It could be a grounding issue.

First check the fluid level after the engine and trans is warmed up.
Then make sure the battery and main ground cable are good.
Then retrieve the codes. You have to have a scan tool that will communicate with the trans and ABS computers.
 

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Discussion Starter · #3 ·
It could be anything related to the transmission or ABS system, (since the AWD light is on). Is the ABS lit up? You would need to retrieve codes from the modules in order to ascertain where to go next. The TCM will flash the light for TCC, AT Temp sensor, incorrect gear ratio, and a few more.

It could be a grounding issue.

First check the fluid level after the engine and trans is warmed up.
Then make sure the battery and main ground cable are good.
Then retrieve the codes. You have to have a scan tool that will communicate with the trans and ABS computers.
I appreciate that big time. ABS is not on yet but I assume it’ll light up on my 20 minute drive to the garage. I’ll leave the code quest to the shop tomorrow and just cross my fingers that the grounding wire is the diagnosis. Would be a huge disappointment if i needed to drop another big chunk of money.. especially after only 140k miles.

I guess the question becomes what’re the odds they diagnosis it correctly? They’re a good shop but aren’t Sub specialists or anything.
 

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Post up the codes they pull from the modules and I'll tell you whether they diagnosed it right.
 

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And the codes from all the modules not just the transmission. That at temp light could be flashing because there's a problem with communication to the ABS module so they need to check the ABS module.
 

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Discussion Starter · #7 ·
And the codes from all the modules not just the transmission. That at temp light could be flashing because there's a problem with communication to the ABS module so they need to check the ABS module.
Much much appreciated. Will try to pull those codes now via that threads instructions.
 

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Discussion Starter · #8 ·
2007 can use the on-board code reader for engine, transmission and ABS codes: 05, 06-09: How To Read Diagnostic Trouble Codes (DTCs)
Nothing.. Blinking “P” for TCM (which user in that shared thread said happened to him too for the TCM screen) but no code ever showed up. Even after a good 2 minutes of waiting. Cycled through and nothing. I’ll have them check ABS tomorrow. Could this further validate the grounding wire hypothetical?
 

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Discussion Starter · #10 ·
Post up the codes they pull from the modules and I'll tell you whether they diagnosed it right.
Alright. Only code from all modules was P1706 for a speed sensor. Shop seems slightly flustered in general. Left it with them for the day. Tranny did lurch once or twice on 25 minute drive to shop. AWD, AT OIL TEMP, and CHECK ENGINE all on when dropped off.
 

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Only code from all modules was P1706
See attached.

Filling in a bit pending @cardoc

That code, when set, should/would cause the AT Oil Temp to flash, and possibly the AWD warning light to be on because the rear wheel speed sensor is requred for the control of the AWD transfer clutch pressure. (The AWD might be turned off due to the absence of rear speed data.)

Usually when a transmission code is determined, a code P0700 is also generated. This in itself isn't a particular fault; rather, the P0700 is a "request" that the CEL be turned on. I'm surprised there wasn't a P0700 as well. It's an ECM, rather than TCM code.

The Rear Wheel speed sensor is on the left (driver) side of the transmission, on the tail section housing. (It's the furthest back of the two sensors on that side of the transmission.) There's a connector at the sensor. The fault could be due to the connector coming out, or not being attached properly.
 

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Discussion Starter · #12 ·
See attached.

Filling in a bit pending @cardoc

That code, when set, should/would cause the AT Oil Temp to flash, and possibly the AWD warning light to be on because the rear wheel speed sensor is requred for the control of the AWD transfer clutch pressure. (The AWD might be turned off due to the absence of rear speed data.)

Usually when a transmission code is determined, a code P0700 is also generated. This in itself isn't a particular fault; rather, the P0700 is a "request" that the CEL be turned on. I'm surprised there wasn't a P0700 as well. It's an ECM, rather than TCM code.

The Rear Wheel speed sensor is on the left (driver) side of the transmission, on the tail section housing. (It's the furthest back of the two sensors on that side of the transmission.) There's a connector at the sensor. The fault could be due to the connector coming out, or not being attached properly.
This is super helpful. Unfortunately, even as I'm educating myself (thanks to you WONDERFUL people), I'm still at the mercy of whatever the shop is aware of. Would hate to offend them by being the armchair expert but ****, this is my **** vehicle we're talking about! One more question: Would a faulty connection at the sensor be enough to cause the tranny to behave strangely? I did get a pretty sluggish/lurching shift from 1-2.

PS. THANK YOU THANK YOU THANK YOU for all of the help so far everyone!
 

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While I can't say definitively, I would think, shifting could be affected without the rear wheel speed data, although I seem to recall reading that the TCM will use the front wheel speed sensor, or the ABS wheel speed data if one of the wheel speed sensors on the transmission fails. cardoc probably has more hands-on experience with this.
 

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I haven't been getting email notices, or I would have responded earlier.

It would be a good idea to have the battery ampere output checked along with the conductance through the main ground. A speed sensor fault should not create a problem with 1-2 or 2-3 shift. A poor power supply will; like bad grounding, a weak battery, or both together.

I've not had to replace a speed sensors on a 4EAT. Harness, yes, when it cracks from deterioration or is damaged from someone working on the car. Which brings to mind that since the engine was pulled, maybe the transmission connectors were disconnected and not reconnected proper. Could be your problem and if the connector is not secured together it may also affect shifting.

So, check the connectors, check the battery ampere output, check the ground cable and satellite ground wires.
 

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Discussion Starter · #15 ·
I haven't been getting email notices, or I would have responded earlier.

It would be a good idea to have the battery ampere output checked along with the conductance through the main ground. A speed sensor fault should not create a problem with 1-2 or 2-3 shift. A poor power supply will; like bad grounding, a weak battery, or both together.

I've not had to replace a speed sensors on a 4EAT. Harness, yes, when it cracks from deterioration or is damaged from someone working on the car. Which brings to mind that since the engine was pulled, maybe the transmission connectors were disconnected and not reconnected proper. Could be your problem and if the connector is not secured together it may also affect shifting.

So, check the connectors, check the battery ampere output, check the ground cable and satellite ground wires.
Once again, you guys are amazing. Hopefully, this thread can help someone else out too.

Shop called and said that after they had disconnected and reconnected that speed sensor, they cleared the codes and drove it "hard and fast" to see if there was any funny business during acceleration/shifting. No weird behavior so they said I could come and grab it. I asked if it could've had anything to do with the grounding cable but their tech said he didn't think so. - I asked them to replace the broken one anyway (it had been broken for some time) - Instead of picking it up tonight, I told them I'd prefer if they drove it in the morning one more time to see if any of the lights came back on. I'll let you know what happens.

Hoping that all of this isn't the beginning of a series of unfortunate events for my outback. Would be a bummer.. Love that thing.

THANKS AGAIN!
 

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Discussion Starter · #19 ·
@cardoc @plain OM okay guys! Hoping you can help out again here. But first i cannot express how grateful i am for the previous advice.

The AT Oil temp light etc got cleared and have stayed off since it’s last visit to the shop. I did notice that it needed ball joints on my drive home however. (It’s always something). So I successfully did control arms yesterday and on my test drive... bing... here comes the check engine. And once again it’s throwing P0420.
I brought it into a muffler/repair shop today. Diagnosis on failed CATs wasn’t conclusive. However, the gentleman said if he replaced em both he thought i wouldn’t get the code anymore. Quote was $2.3k which I’m obviously not going to do.

No sluggish performance, not rotten egg smell, no exhaust leaks up or downstream. Downstream 02 sensor is what’s setting it off. Could it be possible that the sensor just needs replacing? Because if so, that would be amazing. (Btw @cardoc i have read a lot of that P0420 thread you started and appreciate the info but i wasn’t able to find an answer to this question specifically.) thanks guys
 

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Many shops do not comprehend the proper methodology in diagnosing a P0420. The techs/shop automatically want to replace the cat without determining the cause of the inefficiency. You must keep this in mind. Dealer service shops do the same. They see the code, they sell a cat.

Easy way to SEE if the sensor has an issue is to watch it in data. If the feedback is inconsistent varying the voltage up/down and is not a solid waveform, and the up/down voltage coincides with the STFT then you drive it at highway speed with consistent throttle, no AC, (or defrost since that turns on the compressor) and steady speed and watch to see if the feedback levels off or stays inconsistent. If it levels off, change the sensor as this indicates a bad heater circuit. And no, the ECM will not always set a heater circuit code.

The AF and O2 sensors are maintenance items that wear over time and mileage. If you know or think it's the original then it would benefit you to replace both. Rock Auto and get Denso.

If the sensor continues to have a voltage inconsistency varying up/down even under load and steady speed/throttle, then the cat would be bad. It's just one that you would have to replace and it's part of the exhaust manifold. The other one isn't monitored so no shop can tell you if it's bad or not without putting a sensor behind it or testing it in a lab. Forget the rear cat.

I've used a few from these guys and they work.

As long as the engine performance is up to par it will solve the issue with the P0420. If the engine or trans is having issues, it won't and the code will come back up.
 
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