Revisiting the G7 V6 5AT 3rd and 4th pressure switches affecting 3rd gear clutch pack wear.

3rd and 4th pressure switch failure can cause some strange symptoms such as flaring during shifts or even binding when shifting. They likely won't throw a code unless they are open or shorted, even out of tolerance switches likely won't throw a code (unless really bad) or when the 3rd clutch pack has fried or resulting I/O shaft speed out of range brings up a code and a flashing D. It's worth keeping in mind that under certain conditions no DTC will be set, even though the trans is shifting hard and flaring, it appears that the TCM tries to compensate for the failure for quite some time before finally setting a DTC.

Also keep in mind that when the PCM is scanned with an low cost aftermarket scanner you may not see any codes for the transmission (Blinking D indicates that codes are present). You may have to put the PCM into Service Check Signal mode (SCS mode) by grounding terminals 1 or 9 (check the manual) in the DLC  (OBD) connector. Codes are retrieved by observing the flashing D indicator.

The 5AT is not, in itself, a hot running transmission. Heat problems in this trans relate to very high spot temperatures in the clutch packs - one of the reasons fluid goes black "QUICKLY" - and won't necessarily raise bulk fluid temperature to an overheat condition. Heat starts to raise its head when the TC starts hunting in partial lock/unlock states caused by TCM programming, along with low ATF TC/Cooler circuit flow rate caused by valve body design and age, as a result it's exaggerated by things such as driving in stop start traffic with the selector in D and general driving conditions, styles and habits. Honda transmission rebuilders still advise fitting an external cooler in hot climates, but advise against doing so in cold climates as TC lockup can be problematic. There is also a possibility of increased clutch-pack wear under high throttle shifts with low Oil temperature. There are temperature bypass coolers available to overcome locations where both Hot and Cold conditions are common - DERALE Fluid control thermostat (Low tem Cooler bypass) Part #13011 - available on ebay for arount $57.00 US. 

A few of these issues are a direct result of Hondas flawed implementation of phased engagement for the TC and clutch packs. When these transmissions are stripped down you realise the clutch packs are capable of carrying the loads from a V6, but only if Honda had not screwed up valve body design and TCM programming in an attempt to mimic a slush box trans (fail).

The 5AT trans was used earlier than 2003 in other models before the Accord. The main cause of "low" mileage failures in 2003 models was build quality - yes, I know it's NOT the only cause but incorrectly assembled transmissions die early. Graphs and data showing a high number of early failures in 2003 and 2004 for the Accord are skewed a bit because of the discovered poor quality control and incorrect assembly tolerance issues.  We can talk about clutch material being out of spec and other minor changes made between 2003 and 2006 but these have minimal effect on the failure from flawed valve body and TCM logic design. If you had a transmission assembled correctly and depending on your driving habits, driving conditions and regular trans oil changes, a 2003 V6 5ATcan go past 200,000 miles, hell a few have done that with one oil change, sometimes it comes back to driving style and conditions - and style is not something as simple as spirited versus sedate driving.

A number of problems can cause 3rd gear clutch packs to fail, here are but a few reported by Honda transmission rebuilders: Leaking feed tube bushings, linear solenoid mechanical failures, leaking CPC valve bore plugs and malfunction of the 3rd gear pressure switch. Note that last item. Honda transmission specialists confirm that the 3rd pressure switch is critical for the correct operation of these transmissions. If they drift out of spec they will affect switching from clutch pressure during a shift to line pressure in gear and can drastically cut clutch-pack clamping forces. It appears they only have to be out by a few PSI to affect clamping forces and pressure switching to clutch-packs, resulting in slippage with burnt and worn clutch packs failing quickly without the owner being aware of any problem until it's too late.

In 2011 an article appeared in a transmission journal investigating 3rd clutch pack failures in the 5AT. I'd read the article back in 2012 and promptly forgot about it until recently when it was posted in a forum. This article and my experience and testing of the pressure switches now makes sense. Pressure was graphed and monitored in all clutch packs along with 3rd gear pressure switch logic under various driving conditions, it revealed an obvious flaw in shift logic and valve body design in the 3rd clutch circuit. On review, the revealing point of interest is excessive drag in the 3rd gear clutch-pack caused by a design flaw and again, a direct result of Honda trying to overuse phased clutch engagements to make a firm shifting design shift like a slush box. This high clutch drag is very apparent in 4th to 2nd forced downshifts and amplified if you ease off the throttle as the shift occurs, this immediately initiates a 2nd to 3rd up-shift, forcing even more pressure into an already over pressurised and dragging 3rd gear clutch with 2nd gear clutch still locked at or near full pressure.

Of interest is the role of 3rd and 4th pressure switches being used to time clutch engagement/release phasing overlap. As these switches age they need a higher pressure to activate and hold, therefore they also RELEASE at a HIGHER pressure, this will cause an exaggerated "timed" engagement from 2nd while 3rd clutch has even more pressure applied as the 2nd gear clutch starts to release. The TCM thinks that pressure in the 3rd clutch had bled down to the lower design pressure (phased engagement timing) when in fact it has not, resulting in even more drag, heat and damage to the 3rd gear clutch pack. Changing these switches is important. If they have gone out of tolerance it WILL lead to premature and accelerated failure of the 3rd gear clutch pack, a result of design flaws with forced 4-2 down shifts in the 5AT and general gear change clutch-pack overlap programming. As mentioned previously, they only need to be out by a few PSI for increased wear and heat to start damaging clutch packs without any obvious change in apparent shifting, mine were out of spec by over 10 PSI.

Modifying driving style and correct use of the provided "manual gear select lever" can help reduce this problem.

BTW for those who seem to think you manually "change" a gear in an automatic - you can't - and if someone tells you it's a bad thing to manually select a gear, it isn't but, it can be if you abuse or incorrectly do so.  When manually shifting an automatic you are signalling a gear that you would like the transmission to automatically shift into, shift timing and gear change is under full control of the TCM and valve body design - just as the manufacture had intended. Does that mean you can try and shift into 2nd at 100Mph? only an idiot would do that! Due to design flaws in the 5AT, manually shifting under certain conditions may be the only way to bypass forced 4-2 down-shifts and flawed TC logic at low speeds in D from destroying the 3rd gear clutch pack the TC and your transmission.

Note" not all models of the 5AT are affected by all of the design flaws, there are variations and changes through models and years. Some models of 5AT with all these condition were used from 2001 to 2006.

The TC (torque convertor) is often singled out as weak or flawed but in most cases it has been revealed to be, as they say in the classics, not the criminal but actually the victim. As the 5AT ages, there are a number of poor design choices and normal wear items that can cause low apply pressure or poor oil flow through the TC resulting is an overheated or destroyed convertor. Here are but a few reported by Honda transmission rebuilders: Leaking CPC valve bore and plugs in the top accumulator valve body and servo valve body. The pressure regulator valve, lockup control valve and lockup timing valve in the regulator valve body. The torque convertor check valve and lockup spool valve in the main valve body. The Convertor lube circuit with its undersized oil pump assembly. There are aftermarket modified kits that can help overcome most of these problems, another reason to go to someone who specialises in Honda transmissions and who really is across all the modifications needed for these units.

There are still posts about a delay when shifting from N into D in the V6 5AT- The engagement of 1st gear is phased and the design delay is around 1.8 to 2 seconds before hydraulic change over from 3rd to 1st is "fully" complete. This is a design delay NOT a fault in the V6 5AT. That basic 1st engagement delay timing is after moving the lever from N to D and not getting on the accelerator. It varies with oil temperature, oil viscosity and some 3rd gear shift logic learned parameters that also appear to affect N to D phased engagement time - nice one Honda.

Back to the
transmission cooler: My location is mostly warm, around 30C (86°F) most of the time but can get down to 3°C (37°F) for a month or so. I've also had 2 to 3 day trips driving 12 hours stints at high speeds in +46°C (115°F) temperatures. I opted to leave the warmer in circuit (now removed) and fitted a very large High flow Plate and Fin cooler which works extremely well. I changed to fully synthetic transmission fluid years ago when the forums were preaching the "end of life as we know it" if you did not use Honda magic dinosaur oil - and still do by the looks of it (Warranty concerns excluded).