2004 xc 70 turn signal always on

2004xc70 · Post by **2004xc70** » 02 Apr 2012, 15:25

It started with the dashboard displaying "Right Turn Bulb Failure ".
After replacing the front bulb (glass part blown off), the right side signals are constantly in the ON state even with the ignition key
out. Trouble shouted for a couple of days, (pulled all the relays including the CEM) could not find anything wrong.
Drove it to VOLVO today, they told me the CEM is gone. ($1100.00 plus taxes)
Inside the CEM there should be a transistor(blown) or a relay (stuck short) that I could replace.
Anyone has a detailed schematics for the CEM or any ideas how to fix this ?

))))

Thanks

electech · Post by **electech** » 03 Apr 2012, 00:20

Can't help with the module. Take it apart and look inside, you'll probably see what's wrong. Having the skills and tools to repair it is the issue.

What I can say is make sure you don't fry another. Check the ground connections for the CEM and the turn signal cluster. Usually when a module fries, if it isn't a manufacturing defect it is due to open ground. You don't want to find out the hard way when another module fries down the road.

Post by **fazool** » 03 Apr 2012, 06:40

2004xc70 wrote:the right side signals are constantly in the ON state

Just keep turning right. Three rights will get you left and you're good to go

(sorry - couldn't help it)

OK, the CEM is not serviceable and they are pretty reasonable at a local salvage yard. Call erie vovo (no "L") - they have every salvage part there is. They aren't the cheap[est but they run about 1/3 dealer prices and they offer a 6-month guarantee.

2004xc70 · Post by **2004xc70** » 03 Apr 2012, 20:23

electech wrote:Can't help with the module. Take it apart and look inside, you'll probably see what's wrong. Having the skills and tools to repair it is the issue.

What I can say is make sure you don't fry another. Check the ground connections for the CEM and the turn signal cluster. Usually when a module fries, if it isn't a manufacturing defect it is due to open ground. You don't want to find out the hard way when another module fries down the road.

Thank you for your reply.
I have taken the CEM apart, and I have checked every transistor and relay that came in pairs. (Left turn-Right turn)
They all measure the same as far as resistance goes.
I would have the tools, and hopefully the skills as well, if I had the proper schematics for the CEM.I wonder if this is proprietary information for VOLVO. They should definitely give it out to their competitors. Would be a great way to bring them down.

Thanks

2004xc70 · Post by **2004xc70** » 03 Apr 2012, 20:32

fazool wrote:
2004xc70 wrote:the right side signals are constantly in the ON state
Just keep turning right. Three rights will get you left and you're good to go

(sorry - couldn't help it)

OK, the CEM is not serviceable and they are pretty reasonable at a local salvage yard. Call erie vovo (no "L") - they have every salvage part there is. They aren't the cheap[est but they run about 1/3 dealer prices and they offer a 6-month guarantee.

Thanks for reply. Funny. My wife is taking the VOLVO tomorrow and she will take the long way to work, since she will only turn right.....if I could just convince her to take my mother in law along.....
I will try "erie vovo" but I have been worn by my dealer that the CEM has to be exactly the same model and year, in order to have the slightest chance to work on my vehicle.

Thanks

electech · Post by **electech** » 05 Apr 2012, 19:33

The turn signals are CAN-BUS, they do not use any of the relays. (The ticking sound is made by the cluster module, and the emergency module sends a CAN-BUS signal as well).

I just looked on VADIS, and I did find that the turn signals are activated by sending power through shunts in the relay box. The diagnostic for a faulty turn signal says check for a faulty connection or short to ground at the shunt.

The shunts are with the relays mounted to the CEM. My diagram shows the mounting bolt at the top, three vertical lines of relays and 6 small relays along the base. There are six shunts below the vertical line of 7 small relays. The top 2 of those shunts control the turn signals.

Here is the deal with replacement of the CEM:
--------------
Caution! The customer-programmed data must be read off before the control module is replaced. The information must then be entered into the new control module after it has been installed. This is carried out via VIDA vehicle communication.

Note! Remove fuses 11C/32, 11C/25 and 11C/21 before disconnecting the control module connector.
--------------
Not only do you want to get the same part number, you need to have it installed and programmed by the dealer or a competent indy Volvo shop.

Good luck

2004xc70 · Post by **2004xc70** » 03 May 2012, 20:26

Thank you for your help.
Tomorrow the car is going in for a CEM replacement to the local Volvo dealer.
I understand that the signal is coming via CAN-BUS. However that signal cannot drive the turn signal bulbs at its power level.
The turn signal circuit(left and right) is fused by a 30A fuse.In my experience the shunt resistors are only used to determine if the correct amount of current is being drawn from the bulbs (I.E no bulbs are burnt out) There must be a bipolar or field effect transistor that turns the bulbs on based on the CAN-BUS signal. (I remember this from my transistor theory).
I still think it could be replaced if there was a schematic diagram for the CEM" out there".
I am not trying to be argumentative, and really appreciate your response, but I have been dealing with power control circuits for the last 20 years(no automotive application). Turning a bulb on is really not a big deal as long as you know where and what the components are used as a switch.

Post by **DGM** » 04 May 2012, 08:55

Here is the link for the wiring diagram of the vehicule.

https://www.matthewsvolvosite.com/downlo ... iagram.pdf

Page 74 PDF you have the turn signals diagram. Infortunatly the details of the CEM isn't available.

Check all the bulbs (front and rear). Are they of the right type. How good are the contacts in their sockets.

Have you removed them and reinserted one at the time.

Verify if the shunt CSH2 is well inserted, smell it to see if it isn't burned. You can interchange with the left side.

See page 28 PDF for shunt location.

This may look basic but before to spend money on a new CEM I would have a second look at it.

Post by **DavidE7** » 25 Mar 2025, 21:12

The posts above were very helpful for me. The pictures below don't match the words because this is my first post with pictures and I don't have it figured out.

My 2004 XC70 also had this same problem with the right turn signal being in the on positions whenever the battery was connected to the car. My stop-gap solution was to pull the shunt for the right turn signal as shown in the wiring diagram above. This fixed the battery drain problem and allowed me to continue diagnostics and I could operate the vehicle. The prior owner had added aftermarket trailer wiring, and I made sure that was all removed and the splices were returned to factory condition. I tested all three of the right turn bulbs and sockets for an improper connection. Then I made some short male-female spade jumpers to connect the left turn shunt output to the right turn circuit. There are 5 "legs" to the shunt, fewer actually connect, and it is possible to extend these legs with short sections of wiring and plug the left turn signal output from the CEM into the input for the right turn signal harness. I wish I had taken a picture of this setup. This proved to me that the vehicle wiring was fine because when the left turn signal output was connected to the right turn harness, the turn signal lights flashed correctly.

Now I knew the CEM had an electronic fault. My XC70 is a project so I wanted to try fixing the CEM myself.

I removed the actual CEM module from the outer assembly by pulling all the relays and shunts (see YouTube videos for how to prep the CEM for sending in for repairs).

Then I popped off the black plastic cover on the CEM to look at the circuit board.

I was able to visually follow the electrical traces from where the right turn signal shunt connected to a large resistor looking electronic device.

The part number printed on the electronic component told me it is a BUK215 TOPFET. I also learned that this device is used for a lot of different vehicle's turn signal flashing and they are easily available on eBay. Approximately $10 and a week later I had a couple replacement TOPFETs. (Buy more than one in case you make a mistake.)

The next task was to test the replacement part so I unsoldered the power pin on the board to the existing TOPFET and connected the jumper wires to the replacement TOPFET. It worked!

This was a partial picture of the TOPFET jumpers. I forget to document the important steps throughout this process of repairing the CEM...

The attachment 20230930_090552.jpg is no longer available

Now I had to figure out how to remove the defective TOPFET and replace it with a good component. My soldering iron doesn't have enough wattage to heat the entire pad that provides heat sink for the TOPFET so I used a Dremel tool to grind away the TOPFET after carefully unsoldering the connector leads.

Please note that I made one big mistake and the pad second from the bottom was pulled off the printed circuit board because I hadn't melted the solder before lifting on the TOPFET pin.

I ground as much of the copper and solder as possible without going all the way down to the PCB. I then placed the new TOPFET and soldered it into position. I used as much heat and solder for connecting the heat sink back onto the PCB. The one leg with the broken solder pad had to be bent to align with the small stub of the circuit and very carefully soldered. I strongly recommend anybody trying this repair use electronic flux. I have very ugly solder joints because I didn't know how much easier a little flux makes soldering.

Then I reassembled the black plastic cover, the CEM into its holder, all the relays and shunts, and I had functional right turn signals!