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Engine speed sensor

13K views 31 replies 4 participants last post by  Stella501 
#1 ·
Best I can figure, the "engine speed" sensor is more often referred to in the TSM as the "torque converter turbine speed" sensor. That, plus the two vehicle speed sensors, feed into the TCU.

Since they all converge (along with the transmission solenoid controls) in the 20-pin connector B11, what's the trick to extracting individual pins from that connector housing?

Wait... I think I've got it. You pull out the white insert, then you can see the little teeny plastic locks that hold the pins in. Going to have to dig up a dental probe or similar for lifting those locks to release the pins.
 
#2 ·
The turbine speed sensor is not an engine speed sensor. The turbine is in the torque converter, and is, the "driven" side of the converter. The turbine is directly connected to input shaft of the transmission. When the torque converter is not locked, the engine speed will usually be several hundred rpm higher than the turbine speed. Two different measures . . .
 
#3 ·
Yes, I understand that, but it's the closest I could get to answering the question. Maybe you can tell me: If it's not the TC turbine speed sensor, where the he11 is the engine speed sensor that's throwing this AT 23 error?
 
#4 ·
It is unlikely that the ECU gets "engine speed" from a transmission sensor. It is FAR more likely to be one of the engine sensors. I would think the ECU calculates engine RPM from the the Crank-Position Sensor.

Could you please explain this AT23 error a little more? Perhaps if we had more details, we could provide more help. It does not sound like one of the 'normal' kind of errors the ECU would throw.
 
#5 ·
I detailed it in my previous "transmission debugging confusion". In short, here's the symptom:

The problem is totally wonked-out shifting in the '99 Legacy. Within a few hundred meters of starting out, the AT temp light starts blinking. So I do the shifter-and-blink-codes thing and get a 23.
The TSM appeared to send me on a wild goose chase, but grossgary posted:

http://www.subaruoutback.org/forums...ugging-confusion-am-i-stupid.html#post3062025

which suggested the speed sensor (a more sensible answer) as the culprit. Trouble is, there's no such speed sensor to be found.

If the problem originated with the crank or cam sensor, I'm sure the motor would be severely impaired and the ECU would report it accordingly via the regular channels. But that's not what's happening here, and to date I've tried swapping the TCU, the ECU, the MAF, and the turbine speed sensor, without affecting the fault.

Edit: A search here reveals that I'm not the first to experience this confusion. Back in 2011 (before my time here) much the same conversation took place (with a number of the usual suspects):

http://www.subaruoutback.org/forums...-code-23-a.html?highlight=engine+speed+sensor
 
#6 ·
Are you sure the code is 23? Checked more than once to be sure the flashing light is being read correctly? Was there only one code (they read out sequentially)? Is the CEL on when the engine is running? (Does it light when the key is at ON and go out when the engine is started)? Did you check for any OBD codes in P#### format (there could be one, or more, related to the transmission)?
 
#7 ·
I followed the readout procedure exactly, and I reliably and repeatably get a 23 and only a 23. The CEL is not on and there are no OBD codes.
 
#8 ·
Really? Is this turning out to be a stumper? A couple of thoughts...

plain OM, here's what you posted back in 2012:

Phase I

23 Engine speed signal. No signal input above 10km/h
(And I would presume that applies to me, as this car is the 2.5DOHC, making it Phase I, right?)

What's bothering me at the moment is that it says "signal" rather than "sensor", and we've been using the terms interchangeably. I suspect that's a mistake because for all my (our?) searching it seems clear there's no such sensor. Also, as brucep pointed out, it makes sense - especially in the absence of a sensor - that the engine speed is derived by the ECM from its inputs (cam and crank sensors, TPS, MAF, etc.) and it outputs that value to the TCM. Do we know anything about the nature of that interface? From the wiring diagram, it looks like there are eight wires between them, and two of those also go to the TPS. Is there some kind of serial interface, or are they all discrete signals of which one is the engine speed?

What, then, do we make of the "Automatic Transmission and Differential" diagnostic chart that calls Trouble Code 23 "AT Load Signal" and sent me off to check the wiring between the ECM (p. 47) and TCM (p. 20) and to consider failures in the TCM or MAF?
 
#9 ·
The referenced thread was about a 1997, which, unless modified, had the 4AT Phase I. The Phase II was introduced for MY1999 and can be easily identified by checking for the spin-on ATF filter on the left (driver) side of the transmission, just above the oil pan toward the front. The Phase I did not have the external filter. Does yours have the filter on the side?

The limited, known reliable, documentation that I have for pre-2000 has Trouble Code 23 listed as "Engine Speed Signal". Interestingly, the "symptom" for this is "failure to lock up" (i.e., referring to the torque converter); there's no mention of problematic shifting.

Are you confident that the diagnosis chart you have is for the 1999, North American, Legacy Outbacks? Could it be for other than North America? Or perhaps, with 1999 being a transition year, there were some odd changes made to the Phase I's that were still being installed.
 
#10 ·
The referenced thread was about a 1997, which, unless modified, had the 4AT Phase I. The Phase II was introduced for MY1999 and can be easily identified by checking for the spin-on ATF filter on the left (driver) side of the transmission, just above the oil pan toward the front. The Phase I did not have the external filter. Does yours have the filter on the side?
Yes, so I've got a Phase II.

The limited, known reliable, documentation that I have for pre-2000 has Trouble Code 23 listed as "Engine Speed Signal". Interestingly, the "symptom" for this is "failure to lock up" (i.e., referring to the torque converter); there's no mention of problematic shifting.

Are you confident that the diagnosis chart you have is for the 1999, North American, Legacy Outbacks? Could it be for other than North America? Or perhaps, with 1999 being a transition year, there were some odd changes made to the Phase I's that were still being installed.
I'm pretty certain this is the one:

http://jdmfsm.info/Auto/Japan/Subar...ANSMISSION AND DIFFERENTIAL/MSA5TCD99L508.pdf

So if your previous discussion was about Phase I and mine is Phase II (judging from the filter), we're back to this being a problem with the AT LOAD SIGNAL from the ECM to the TCM.
 
#11 ·
Strange that the Trouble Code 23 AT Load Signal appears only in that document. I had a look at the corresponding diagnosis sections in earlier and later years from that same web site, and none have this. It seems to be only 1999.

But I also noted that the document refers to both the 2.2 liter and 2.5 liter engine. I thought only the 2.5 was used inNorth American-built Legacys and Outbacks in 1999. Why would there be the separate reference to the 2.2, and the related Trouble Code 45?

Very strange . . .
 
#12 ·
I was kinda thinking along the same lines. As I said, I can see the troubleshooting guides considering bad wiring or a bad TCM (though it seems to me that the ECM - as the source of the signal - being bad is as good or better a candidate than the TCM), but the MAF sounds like crap to me. If it's bad the ECM is going to raise a P code. So I'm wondering what the subsequent years say about the 23 - maybe the MAF thing is a mistake and they have a better suggestion to make in later versions of the manual. What do they say about it?

As for the 2.2, it doesn't strike me as all that weird, especially since they explicitly refer to the California 2.2 .

Edit: But the reason this doesn't make any sense is that I've replaced the TCM, the ECM, and the MAF, and it didn't change anything. Granted, they were junkyard parts, but I don't think that necessarily negates the value of the exercise. This is making me a little crazy - I just don't know what to try next, other than throwing the scope on the AT LOAD signal just to see what it's doing.
 
#13 ·
So I'm wondering what the subsequent years say about the 23 - maybe the MAF thing is a mistake and they have a better suggestion to make in later versions of the manual. What do they say about it?
I had a quick look at the AT "diagnostics" section for 2000 that is on that same web-site and it doesn't seem to have a Trouble Code 23 at all, or any AT "trouble" identified as "AT Load", or relating directly to the MAF sensor. Earlier years (e.g., 1998, 1997) do have a Trouble Code 23, but it's for the "Engine Speed Signal". It's the absence of a listed code 23 in the later year where the Phase II should be the AT that is puzzling in light of the fact that you are getting that code indication.

However, using the 2000 documentation (http://jdmfsm.info/Auto/Japan/Subar...smission and Differential/MSA5TCD00L18851.pdf), there is a Trouble Code 45 — INTAKE MANIFOLD PRESSURE SIGNAL. This might be going off on an unrelated tangent, but the wiring diagram with this, and troubleshooting guide, refer to connections between the ECM and TCM that are identical to the connections in the 1999 document for the TROUBLE CODE 45 — AT LOAD SIGNAL (2200 cc CALIFORNIA SPEC.
VEHICLES).

In 1999, both code 23 and 45 appear in the document, and both refer to the AT Load, and the MAF. But in 2000, the code 45 refers to the MAP. And in both years, the TCM connection is B55 pin 20. Could this be an error in the 1999 paper; should it have read MAP rather than MAF?

(Granted, if the MAP is faulty, one would expect an engine trouble code for the MAP. But, then, does your 1999 even have a MAP sensor . . .?)
 
#14 ·
I share your apprehension about going down a rabbit hole, but as long as it's the only one we've got...

The similarities are indeed interesting, as is the possibility of a MAP/MAF typo. But I don't see a MAP sensor in the 1999 schematic - in its place (on the drawing) is a "Boost sensor". I don't know what that is or where to find it, but it sounds suspiciously like it could be a MAP-sorta thing.

Where on the manifold would one look for a MAP sensor?

Edit: Is it that little mess of stuff tucked under the manifold on the passenger side? The docs (1999 Engine Section 2-7) refer to it as: (33) Pressure sensor, and (34) Pressure sources switching solenoid valve. No... I don't think so. Whatever that is, it appears to only be a solenoid with a two-contact connector, not the three-pin connector the schematic says the "boost sensor" has.

So where the he11 is this boost sensor?
 
#15 ·
MAP is mounted on the intake manifold, just downstream of the throttle plate.

In that diagnostic section there's charts for the input/output connections at the ECM. I don't see a MAP or BOOST listed, but there is Atmospheric Pressure Sensor. Perhaps that's the same as the Boost sensor you have. The MAP is not measuring atmospheric pressure (except when the engine is off), so tend to doubt it's the MAP. Perhaps there isn't one . . .

. . . lost down the hole .
 
#17 ·
MAP is mounted on the intake manifold, just downstream of the throttle plate.
On the '99 the transducer isn't there. Instead, there's a little air hose fitting that moseys off to this little array of solenoid valves and the boost sensor. This is a real hack.

In that diagnostic section there's charts for the input/output connections at the ECM. I don't see a MAP or BOOST listed, but there is Atmospheric Pressure Sensor. Perhaps that's the same as the Boost sensor you have. The MAP is not measuring atmospheric pressure (except when the engine is off), so tend to doubt it's the MAP. Perhaps there isn't one . . .
Well, how does this sound for a theory: I think what's going on here is that they're getting double-duty out of that transducer - flip the solenoid valves one way and they're measuring manifold pressure; the other way and they're measuring atmospheric (the valve mounted out next to the sensor does, after all, appear to vent to ambient). So I'm half inclined to think that it may not even be a failure of the sensor - it may be that one of those valves is misbehaving, the wrong port (or both, or none) is getting connected to the sensor, and the ECM is forwarding a bad reading to the TCM.

. . . lost down the hole .
Maybe, but as long as we're down here let's try to find something to kill and eat.
 
#16 ·
Ah, not on the '99, it isn't. It's that little pile of junk mounted on the shock tower, between it and the air cleaner - the solenoid and sensor are both on that bracket. I unplugged the sensor and sure enough it threw a P0108 code - "MAP/Barometric Pressure circuit high". So that's what and where they call the "boost sensor" in a '99. Question is: Does that have anything to do with my problem?
 
#18 ·
I wouldn't have thought they would measure MAP remotely. But looking up the code in that same diagnostic paper, it shows the "pressure source switching solenoid valve" and what looks as if it might be a representation of the vacuum line between the solenoid and the sensor. (Also now see the sensor and solenoid in the diagram on page 2-7 [T2C2]. )

But, presumably, going back to your earlier approach, if the solenoid, or sensor, were malfunctioning, wouldn't that affect the ECM's use of the data as well? Shouldn't that lead to an MAP sensor-related trouble code?
 
#19 ·
Engine 'load' is measured using the "pressure switch" (MAP sensor). The ECU can calculate the 'load' on the engine based on the difference between atmospheric pressure and the intake-manifold vacuum.

On some Subies, the pressure-switch has a solenoid switch on it which the ECU can manipulate to utilize the pressure-switch to perform multiple functions. (by routing its input from different areas of the engine.) In this way the pressure-switch is used to measure multiple things.

I have a couple Haynes manuals for Subaru. There is a description how to test it off the vehicle using an ohmmeter and a handheld vacuum-pump. There is a graph showing the curve vacuum -vs- resistance.

Personally, I would think a problem with measuring engine-load would NOT be a faulty pressure-switch and instead a broken or mis-routed hose. (perhaps even the routing solenoid.)

I am not sure if faulty pressure-switch itself would always throw an error-code.... (how does the ECU know if it is being fed bad data?)
 
#21 ·
. . . I am not sure if faulty pressure-switch itself would always throw an error-code.... (how does the ECU know if it is being fed bad data?)
Probably not if the data is within a valid range.

Many of the trouble codes, especially in the earlier models, are simple "wiring open" or "wiring shorted", codes. In these cases, the OBD tests the voltage at a sensor's input to the ECM or TCM. If all is well, the voltage will be within a specified range. For circuits using 5 V, that might be between one one Volt and 4.5 Volts. Any voltage within this range will not trigger a code, even if technically, it's nonsense. However, if the voltage is below the lower threshold, or above the higher one, the OBD interprets this as a short or an open circuit, and triggers the related code.

The trouble codes mentioned in this thread are all "detects open or short circuit . . .".

And we know that a code is being set --AT Trouble Code 23. The problem seems to be, wiring to/from what?
 
#20 ·
On your 99, according to Haynes, the pressure-switch is mounted over the front-right tire inside the engine compartment. It has several small hoses and an electrical plug. The routing-solenoid is nearby.

BTW: On the turbocharged engine, this same sensor may be called the "boost sensor" because it can also detect pressure in the intake manifold. (I have a turbocharged engine myself :) )

It is only two pins on the connector because it simply changes resistance in response to pressure-changes.
 
#23 ·
I wish to make correction to my past append. The pressure-sensor indeed has THREE pins...... GND, +5v, and signal. I believe the signal should be about 3v at idle (high vacuum) --- then smoothly change to 2v as engine RPMs rise. (lower vacuum)

Also, I am starting to think that the goofy error you are seeing may NOT be telling you that the engine-load sensing is bad.... Instead, it may be the computer is trying to tell you it is getting conflicting signals. (ie..... The sensors in the xmission do not jive with the sensors on the engine)

This does NOT necessarily mean the engine-pressure-sensor is bad.... just that its signal does not match what the xmission is doing. I guess I am saying that more troubleshooting is in order.

If it were me, I would hook up a vacuum-meter to the intake.manifold and check for 'normal' readings. Also, I would inspect all vacuum hoses for cracks (or just replace them to make sure)
 
#22 ·
Been away since my last posting - made a trip to the junkyard for some solenoid valves and pressure transducers, went out for a little sail with my girls, some shopping, a couple of burgers (though the dog just ate my last one... grrr...). I see that in my absence you guys have covered some of the salient points, and I think you're pretty much on-base, except that the transducer itself is an active three-terminal device (not two) that needs to be powered and outputs a signal proportional to the input pressure - it's not just resistive.

I too think the ECM isn't bothering to sanity-check the values it's forwarding to the TCM. If I had to guess, I'd say the guys writing the code for each module couldn't come to agreement about who should be doing it (You do it. No, screw you, you do it.) And now that I have a reason to learn this bit, the information is everywhere - in the Haynes manual, on the emissions sticker, etc. It's just that there's little consistency in the naming conventions for the parts, particularly the pressure sensor itself.. Anyway...

I just tried swapping in a sensor and the switching valve. No change. Although I got a couple of them from the yard, I haven't yet swapped in the other solenoid, the one under the manifold. I don't think it's implicated, as it's a purge valve of some kind, according to the emissions sticker.

However, the manifold vacuum line that runs to the switching valve also goes to some sort of pressure regulator that's mounted at the aft end of the passenger side fuel rail. Any idea what that's about?

Edit: Oh, I see. That's actually the fuel pressure regulator. Guess that makes sense - manifold pressure drops and it raises the fuel pressure. Probably not an issue, but it does suggest I should take a look at the manifold vacuum.
 
#25 ·
That is the MAP sensor and EVAP fuel tank pressure sensor. That's what the solenoid switches between. BARO or atmospheric is what the ECM reads on that sensor before the engine cranks. Yes it is called a boost sensor because that is how it translates into Japanese Manglish techno jargon. And that is what it does on a turbo. And try reading Kia manual or scanner. Their favorite phrase is "Is Not Exist". If you can wait I'll look the code up on Mitchel and IATN for you. 99 Legacy if I have followed this correctly???
 
#26 ·
Looked it up, found one 99 with 23. it had a loose intake manifold. All the main engine harness and trans harnesses ground to the intake. So make sure the intake is tight (which could throw a lean or MAF code) or the MAF isn't getting grounded. then find all the 10 mm bolts with a bunch of wires on eyelets and take them off and clean them. And look around under the hood and fenders, there are more. Then check all the trans, EcM, TCM plugs for "green death" . Lastly, and easily said than done, you need to check for continuity on the engine speed signal wire, then junp one end to ground, one end to a 7440 bulb, and jumper that to the battery. You need continuity under stress. You can have cont. on your meter, but you could have a rubbed out or chewed out harness, where you got one strand, but it can't carry enough load. I think you have a basic electrical issue. If this fails you need to have someone scan it and get the P07ish code, it will be more specific for you searching.
 
#27 ·
...... find all the 10 mm bolts with a bunch of wires on eyelets and take them off and clean them. And look around under the hood and fenders, there are more. ....
This is good advice for ANYONE with a vehicle over 5 years old. The grounds under the hood are exposed to the worst possible conditions for electrical connections and tends to corrode over time. Roadsalt gets in there and corrodes things all summer long.

Since the ECU relies on minute voltage readings to do its job. A poor ground connection is the #1 cause for intermittent, flaky problems in a car.

This is what I do to every vehicle I ever owned -- Locate every ground-point I can find and pull them off, use dremel-tool with wire-wheel to clean them. **Solder** the wires to the connectors.

You may be surprised how many factory ground connections still have PAINT under them. They rely on a star-washer to poke thru the paint. This is NOT a reliable way to make a ground connection.
 
#28 ·
You're all probably right - this may wind up being a flaky ground problem after all, though I'd be surprised if it came down to a loose bolt. I did a block swap not long before this problem cropped up, so everything was carefully torqued. But I can't discount the possibility that a wire might have fatigued at a crimp lug with all the moving and wiggling of harnesses that accompanies major work.

Stella501: I'm skeptical about the "can't carry enough load" part. This engine speed signal travels from the ECM to the TCM, so it's a high-impedance signal that doesn't need a lot of current-carrying capacity. Oh - and I mentioned previously that there's no CEL and there are no OBD codes to read. It's only the TCM that's reporting a fault (beside it obviously not shifting right).

I've got to step away from this thing for a day or so while I get the engine+tranny back in the '95, but I'll update when I've got something new.
 
#32 ·
YAAAAY It's the little things that'll just root ya. so to all who are watching this thread, and you got multiple electrical/tronic failers, find out what they have in common. And surf over to Gen 1 for my rear power outlet.
 
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