mikerayvt Posted October 8, 2009 Share Posted October 8, 2009 Hi, My Subaru Outback 1999 experienced a very little but noticable harsh shift at 25mph in cold mornings after the rebuilt transmission replaced. The service couldn't find a problem and thought it was ok as long as it's warmed up first. Oil Temp High came on a couple of times in the past year and went away when stopped and restarted. Now it came on all time and gears shifted too harsh at 40 or 45 mph. With a given instruction for P0710, I was able to locate a problem with voltage input to the temp sensor. According to the paper, voltage should be 2.9 - 4.0 volts but I got 1.6 volts even the sensor resistance was within spec. TCM replaced didn't fix and got the same result. Temp Sensor replaced didn't fix. Wires replaced between TCM and AT didn't fix. Added a Temp Sensor to the exterior surface (deep concave) of Transmission with new wires to TCM (cut wires to Temp Sensor that was inside AT) solved the problem and driving good for a couple of months. Now weather is turning to cold soon and need to fix it permanently. I want to know about voltage input to Temp Sensor from TCM. Is the instruction wrong? or Is a new TCM bad? Does the wire assembly inside the transmission need a replacement? Thanks! Link to comment Share on other sites More sharing options...
Legacy777 Posted October 8, 2009 Share Posted October 8, 2009 If you've replace the TCM, the wiring from the TCM to the temp sensor, and the temp sensor itself.....I can't see your problem being any one of those three. I would check your grounds. Is the temp sensor a 1-wire or 2-wire sensor? The 1-wire sensors ground through the trans and if the grounds are not right, that may cause a problem. Link to comment Share on other sites More sharing options...
mikerayvt Posted October 8, 2009 Author Share Posted October 8, 2009 Its 2-wire. I have put a ground wire between the transmission and the firewall before and it didn't help. Normal wires route from TCM connector B55 to transmission connector and from transmission connector going into transmission to temp sensor connector. I tried new wires. I cut wires just after TCM connector and cut wires just out of tranmission and connected new wires between them and it didn't help. Only a temp sensor temporarily mounted on transmission with new wires straight to TCM connector works. No Oil Temp High and no harsh shift. The problem according to the diagnosis instruction is that voltage across the temp sensor is too low but my car works fine. (I measured temperature with an IR gun on the transmission surface and resistance across the temp sensor and they are good (about 180 deg and about 300 ohms). Voltage across the other temp sensor inside is same (too low). The voltage with a different TCM is too low too. It's from 2005 Mitchell Repair Information Co. If the voltage is normal, then wires inside transmission are bad but I am not sure about the instruction. I tested voltages like 10 times spring and summer. Link to comment Share on other sites More sharing options...
Legacy777 Posted October 9, 2009 Share Posted October 9, 2009 Hmmm....that does sound a little funky. Probably as you indicated a wire inside the transmission. But without digging inside it'd be hard to verify and test. Is the temp sensor internal or external to the transmission? Link to comment Share on other sites More sharing options...
mikerayvt Posted October 9, 2009 Author Share Posted October 9, 2009 The temp sensor is inside but it is off since another temp sensor is temporarily mounted on the surface outside and it's active. I added it to isolate a root-cause problem. When a problem is found, it will be removed. A pair off wires are also added between TCM and the outside/temporary temp sensor. The wires to the inside temp sensor is cut off. If I reconnect the inside temp sensor, it would flash "Oil Temp High". It seems confusing. Does it? I briefly tested circuit between the connector outside the transmission and the temp sensor connector inside and they were ok. I didn't test wires to ground (make sure they are not short to ground). They were not at operational temperature and I didn't move wires around to see if circuit becomed open or short to ground. I didn't expect it until I realized that this section is the only remain to test??? It could be somewhere else. If the wire inside the transmission is causing the problem, would wire replacment be easy without having the transmission taken out? Is there anybody who knows about voltage spec for TCM and temp sensor? Link to comment Share on other sites More sharing options...
OB99W Posted October 9, 2009 Share Posted October 9, 2009 (edited) [...] Is there anybody who knows about voltage spec for TCM and temp sensor? Is this the information you're working with: http://ww2.justanswer.com/uploads/ebrock63/2009-03-21_162915_testing.pdf ? That info seems to be flawed. I believe that step 8 should say ''If voltage is not 2.9-4.0 volts, go to next step. If voltage is 2.9-4.0 volts, go to step 12.'' EDIT: I checked further. Actually, the error in step 8 apparently is that it says ''Warm-up ATF to operating temperature''. The 2.9-4.0 volt range (what I have says ''3.45 +/-0.55 volts'') is for the ATF at 20 deg C, 68 deg F (not operating temp). The lower voltage range in step 9 is for the ATF at operating temp. You'll notice that step 9 says that if the voltage is 1.0-1.4 volts that the ''circuit has returned to normal condition''. I suspect your measurement of 1.6 volts is probably close enough, given that the sensor isn't mounted where it can reach the actual temp of the ATF. Edited October 10, 2009 by OB99W More info Link to comment Share on other sites More sharing options...
mikerayvt Posted October 13, 2009 Author Share Posted October 13, 2009 It makes a sense! Yes, I used that info sheet. You're awesome! You answered to my question. I reviewed my test results and did one more test after the transmission temperature was lowered to 80 deg F. With a new wire connection to the temp sensor outside, I measured voltage between two wires with my little voltmeter. The temp sensor resistance is 1500 ohms, the voltage read 1.2 volts when the volt range is 9V. When I switched range to 1.5V on my voltmeter, it read .15 volts. Something wrong. The volts were supposed to be about same in two different ranges. I tested a 1.5 volt battery with my voltmeter and the reading was same in the both range. I suspect current is weak? I swapped TCM and the result was the same. If you read my replies/answers in justanswer.com, it's same result. (9/6/09 7:38pm) An expert asked me to measure voltages that were inputs to TCM and they seem ok. I think the connector to TCM is bad or maybe both TCM's bad. I could take the cover off and measure some points inside to test the terminal connection. Is it required that the TCM box is grounded all times? Is there any variable or control to vary the voltage to the temp sensor? Tomorrow is my appointment with Subaru service for my car. Maybe I leave it to them. Link to comment Share on other sites More sharing options...
OB99W Posted October 13, 2009 Share Posted October 13, 2009 One thing that can affect voltage readings in some circuits is voltmeter ''sensitivity'', given in units of ohms-per-volt (ohms/volt) relative to the full scale reading for a particular range. Inexpensive analog multimeters often have low sensitivity, about 1,000 ohms/volt. With such a meter, low ranges in particular can significantly affect readings if the circuit has resistance of the same order of magnitude. Usually the meter's sensitivity (which can be different for DC and AC) is printed in a corner of the meter scale. Better analog DC meters have sensitivity of about 20,000 ohms/volt (20kohms/v), adequate for most automotive circuit testing. Electronic types (VTVMs, FET-VOMs, DMMs) often have input impedance of 10,000,000 ohms (10Mohms), independent of the range they're set to. From your description, I suspect the meter you're using has relatively low sensitivity. If that's not the case, then the circuit itself may have a high-resistance connection. Link to comment Share on other sites More sharing options...
Legacy777 Posted October 13, 2009 Share Posted October 13, 2009 I'd tend to agree with 0B99W. You may need a better meter. The chances of both TCM's being bad are pretty slim. Anything can happen, but chances aren't too great. Link to comment Share on other sites More sharing options...
Fairtax4me Posted October 13, 2009 Share Posted October 13, 2009 Have you checked resistance through the wiring between the TCM and the sensor? Link to comment Share on other sites More sharing options...
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