CVT Diagnostic Manual

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CVT Diagnostic Manual

Post by volvodspec » 12 Aug 2011 09:48 pm

This practical-experience based manual is written for all V300’s from modelyear 78 till the very end of the V300’s production models. If you own a modelyear 76-77 CVT vehicle, please read the final bit of text at the very end of the manual first. We know that not all of the info in this manual is exactly the same as the Volvo documentation and Volvo doesn’t even list half the information in this manual, BUT; all info on here is what works in the field, it’s easier to diagnose about 99% of the possible problems and without too much hassle using this manual.

Follow these directions if you feel your CVT is producing more revs than necessary under driving at constant speeds, what; follow these directions anyway, your car could be out of “perfect” running order for years without you or your mechanic knowing it! If your CVT produces more revs during take off from a standstill, please consult the “CVT clutch diagnostics section” (is yet to be made, will be hyperlinked here once it's written)

What revs belong to which speed for a Volvo 300 CVT vehicle?

30mph @1800rpm 50km/h @ 1800 r.p.m.
40mph @2300rpm 60km/h @ 2100 r.p.m.
50mph @2900rpm 70km/h @ 2500 r.p.m.
60mph @3500rpm 80km/h @ 2900 r.p.m.
70mph @4100rpm 100km/h @ 3600 r.p.m.
80mph @4700rpm 120km/h @ 4400 r.p.m.
90mph @5300rpm 130km/h @ 4700 r.p.m.

You get these figures only with a V300 on which:
- The clutch doesn’t slip
- The vacuumsystem is working correctly
- The gap between the pulleys of the secondary gearbox is within spec

On further notice, the size of the rear tires can have a big influence on the revolutions, especially at higher speeds. If the revolutions at greater speeds are too high, the gap between the pulleys of the secondary gearbox is the main suspect (please consult the “checking the gearbox air gap section” (is yet to be made, will be hyperlinked here once it's written).
When the revolutions are too high at the above constant speeds the fault is most likely to be in the vacuum control for the gearbox.

Checking the vacuum system

We start with checking the vacuum system parts under the car, you can check these at the EMV. This is the thing under the bonnet near the right hand side of the car at the strut topmount.

Connection A: this is the connection of the “gear up” vacuum
Connection B: this is the connection of the “kickdown” vacuum
Connection C: this is the source of all the vacuum, and comes from the base of the carburettor
Connection D: this is the return connection and this hose goes to the air filter housing

First, take hoses A and B off (note that A is a smaller diameter hose than B!!!) turn it on the EMV first, then pull it off. Clean the ends off, blow in it (absolutely don’t use compressed air!!!) and try to hold the pressure, hold it under pressure for about 10sec.

Result 1:
The pressure buildup becomes greater when blowing, after 10sec all air comes back out of the same hose. If you get this with both result A and B everything under the car is fine!
Result 2:
On both hoses you can get a pressure buildup, but after 10sec the pressure buildup is gone. This means a small air-leakage in the primary gearbox, a small puncture of a membrane or a leaking seal
Result 3:
1 of the 2 hoses gives result1, the other has no resistance and you don’t get pressure buildup. This means one of the hoses may have failed or is loose.
Result 4:
Both hoses have no pressure buildup, when you blow in one hose the air comes out of the other. This means a mayor leakage in the primary gearbox, most likely one of the membranes is ruptured.

Important info before we proceed
Beware that the electrical system switches the kickdown OR gear-up side of the EMV, it will never activate both at the same time. While knowing that, electrically the kickdown-circuit gets priority over gear up, hence why the kickdown circuit can be activated while the car is driving under “ gear up” conditions and you activate the kickdown circuit for overtaking or using the gearbox as a engine brake in the mountains. In short words; if the EMV is electrically activated on the kickdown side, you will never get vacuum OR voltage on the coil of the gear-up side of the EMV.

Checking the EMV
Now the hoses A and B of the EMV are loose, we can check if the EMV itself is working properly.

The connections A and B are different, connection B the kickdown vacuum is unrestricted this is because for kickdown you want a quick response of the gearbox to select a lower gear so you can overtake.
Connection A the “gear up” vacuum is different. In the factory the EMV’s got a restriction on the A side to allow around 400mBar through, this is to make sure the car doesn’t want to go from 1st to 5th gear instantly when taking off and allows a efficient and smooth gearchange when driving, as far as this automatic wonder is comparable to a manual car o fcourse!

If you take a look at the EMV the 2 sides have different wire colors, at the side where hose A is connected, there’s a grey and a green wire. Where hose B is connected, there is a brown and a yellow/green wire.

To check side A, run the engine in N, press your finger gently to the connection on the EMV; now raise the rpm’s to above 1800, this connection should now suck noticeably by your finger.
To check side B, run the engine in N and let it idle, switch on the low gear hold switch inside near the gear lever and you should hear it suck noticeably.

Result 1:
Both connections suck as above, this is good news as the vacuum system seems to be OK! For further problems that don’t occur all the time, consult the electrical section.
Result 2:
One of the connections sucks from the moment you start the engine; or
At one of both tests you hear the valve “click” but the connection doesn’t suck, in this case one of the rubber valves inside the EMV is broken. You can buy a EMV rebuild kit to sort this problem out.
Result 3:
At one or both tests the EMV doesn’t suck and the coils don’t click, you need to consult the electrical section.

Checking the electrical section
We start with checking the Tachometric relays inputs.
The tachometric relay is located on the same bracket as the EMV, it’s the black box with a 8-pin connector, it looks like this (pic is from a DAF55 though!)

Now we check a few connections of the 8-pin connector, note the angular sides to make sure you take the right pin!

With a multimeter, we do this test with the – wire to the negative pole on the battery.
- Connection 4: earth (resistance measurement, ideal is 0Ω)
- Connection 5: feed (volts measurement, ideal is the same as the battery
- Connection6: switched earth of the kickdown circuit (resistance measurement, ideal is 0Ω)

The kickdown circuit consists of 3 switches, these are the low gear hold switch, the brake pressure (20Bar) switch and the kickdown switch (at the accelerator pedal)

The low gear hold switch is located near the gear lever and easy to find. The other switches are found here (note that the car’s on the pics are left hand drive; for right hand drive it looks the same but is located slightly differently!)

These 3 switches are all on the same circuit, to check these we let the multimeter connected to connection 6 on the 8-pin connector of the tachometric relay
Operating one of the switches must result in a infinite resistance on the multimeter gauge, as soon as you release the switch the multimeter must say 0Ω again (compare this to holding the pins of the multimeter to each other and see how quick it goes back to 0Ω
- Low gear hold switch, switch on and off
- Brake pressure switch, apply the brakes hard
- Kickdown switch, at full throttle (not with the engine running!)

A temporary high resistance/sticking resistance after letting go of the switch is NOT good because this will cause it to stick while driving.
Besides mounting new switches if one of these are broken, you can also rule them out electrically as a temporary solution. For the brake pressure switch, interconnect the yellow and red wire with another wire. For the kickdown switch, go inside to the switch at the top of the accelerator pedal (remove black isolation panel under dashboard to get there if present), connect the yellow/green wire to an earth.

Electrical check of the tachometric relay outputs
There is a possibility the tachometric relay can stick on an internal relay, put the tachometric relay back to the 8-pin connector and do a volts measurement to the B side on the yellow/green(+) and brown (-) wire. Again apply the 3 switches the same as above and this time each coil needs to reach 12V and instantly drop if you release the switch. If it stays 12V for a while or doesn’t respond open the tachometric relay and note the big relay at the middle, carefully check the larger solder pieces for cracks around the pin and if necessary solder them again.

Now we check connection A on the grey (-) and green (+) wire the same way, but to get 12V on these, you need to start the engine in N and raise the revs above 1800rpm

Result 1,
You get around 12V above 1800rpm, check the coil is working by feeling on the coil to note it slide on and off internally.
You get around 12V and the coil is not working? Open the EMV and de-solder the diode, now check the diode for blocking in the right way and check the coils resistance, this should be around 33Ω
Don’t get around 12V above 1800rpm? First follow the directions at result 2 because the diode/coil and the solution for result 3 are electrically related and these can also be broken.
When that’s sorted, open the tachometric relay at the connectors side
We’re looking for the end-transistor which is most likely broken, see the arrow on the pic below:

This component is the transistor that gets the current to the gear-up coil, when this transistor is switched off without the safety of the diode in the EMV this transistor is notorious to fail (trained electricians know that this is the result of self-induction) the diode can fail due to its location being exposed to heat.

A new transistor is available at a well sorted electronics/radio shop for pocket money.
You’re looking for the BC33725 model, solder this in exactly the way the original one was positioned, or leave this to a professional

Next is a pic of how to add another diode parallel to the one inside the EMV as a backup-protection for your new transistor, note the white stripe or blocking direction of the diode!

Tachometric relays with this modification very rarely fail on the “gear up” side again so it’s worth doing it!!

The reason why this diode wasn’t factory-present in the tachometric relay is that the tachometric relay was a “black box” item, whereas the EMV was specially made for the Volvo300Series.

For modelyear 76-77 343 owners only!

All info on the EMV (excluding wire colors) and the gearbox are the same as written in this manual. Your car wasn’t yet equipped with a tachometric relay but with a micro switch on the carburettor. enough info on this is in the CVT- green book, other specific modelyear 76/77 questions can be asked on the forum.

We hope this manual was useful to you, problems or following questions can always be asked on the forum.
Volvodspec- Anjo
Technical Commission of the Dutch Volvo300Club
Last edited by volvodspec on 23 Nov 2011 01:47 pm, edited 1 time in total.

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Alex Laidlaw
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Joined: 10 Nov 2009 01:54 pm
Location: Oxford and Worcester

Re: CVT Diagnostic Manual

Post by Alex Laidlaw » 17 Aug 2011 07:35 pm

Thanks for this Anjo. I need to get round to getting my vario sorted :)

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Re: CVT Diagnostic Manual

Post by volvosneverdie » 18 Aug 2011 08:47 pm

Sticky it mods!

Great work Anjo.

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Joined: 18 Apr 2012 05:31 pm

Re: CVT Diagnostic Manual

Post by hyperkv » 18 Apr 2012 06:03 pm

hello. I'm new Volvo 340 with cvt owner, and having hard time... well rpm's for driving seems way too high.... followed your manual, and found out that for high gear valve(where's pipe A) both wires are about same as battery, even with not engine on. when i start it and get rpm's higher(i suppose than it should start some suction(change gears)) one wire drops to about 2V an it clicks as it turns on, suction works, but quite weak...
well experimented- plugged all wires off from emv and clutch valve, nothing changes. Also pulled off all pipes- both for cvt and clutch(after valve)- no response- all works like usuall...
diaphragms are all OK, in connector plugs NR. 4 and 6 are showing resistances 08.9 (bolt on 200ohm), NR.5 shows almost same voltage as battery . any guess? :)

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Re: CVT Diagnostic Manual

Post by volvomania » 12 Dec 2013 09:09 am

The overhaul kits for the EMV and the tach relay can be ordered from Born Built Beauties (
It is actually quite easy to do.
Life is a journey, so sit back and enjoy the ride!

Born Built Beauties: Parts keeping our cars on the road!

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