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Eric, Automotive Repair Shop Manager
Category: Volvo
Satisfied Customers: 32060
Experience:  20+ yrs. experience as repair shop manager and technician.
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I've been having an issue with my 2004 XC90 T6 AWD. The

Customer Question

Hi, I've been having an issue with my 2004 XC90 T6 AWD. The A/C blower fan has been working intermittently. I ordered a new fan, but after doing some troubleshooting with the help of a tech on Just Answer, I realized that the fan is fine. Sometimes the
fan speed will change without me turning the dial. Sometimes I will drive to a place with the A/C blower fan working and park, but when I return to the vehicle and start it, the A/C kicks in but the blower fan doesn't turn on. I figured that maybe the climate
control module on the dashboard was defective, but sometimes the entire dashboard will die while I'm driving, or it may go on and off several times. If it stays off, once I turn the engine off and turn it back on, then everything comes back to life. Also,
if it stays off, my turn signals, power windows and door locks do not work. I have to turn off the vehicle, remove the key and then turn it back on and everything starts to work again.
Submitted: 1 year ago.
Category: Volvo
Expert:  Eric replied 1 year ago.


I am sorry that you have not been helped yet. I just came online and saw your question

Sounds like there may be a problem with the CEM(central electronic module), but would like to have the last 8 of the vin to pull the wiring schematics for all the systems involved

Customer: replied 1 year ago.
Customer: replied 1 year ago.
By the way, after I hit 65 MPH, my transmission doesn't change to a higher gear as it used to. So instead of dropping to 2500 rpm, my engine stays at over 3000 rpm, are the issues related or is my TCM (transmission computer) also shot?
Expert:  Eric replied 1 year ago.


Did the transmission issue begin at same time as the ac blower issue and dash issue, or did it just start happening

Customer: replied 1 year ago.
Transmission issue existed before
Expert:  Eric replied 1 year ago.


Ok, looking over all the diagrams, this is going to be the CEM, with a slim chance of a wiring short going to it, so I do recommend having it tested with a scan tool before having it replaced and new one programmed in order to verify it is faulty and not a wiring issue.

The transmission is a separate issue. This may be in the tcm, but also could be the tcc solenoid or the torque converter clutch itself.

Customer: replied 1 year ago.
Would I have to go to the dealer to have it checked with a scan tool? The fact that it's intermittent tells me that the electronics may be on the fritz, and the online posts from other users would seem to indicate that. I'm a home automation/network engineer with college training in both electronics and networking so feel free to go technical on me. Is the module something I could change myself and then ask the dealer to program it. I also forgot to mention that when this problem started, the air bag and brake service light came on and have not turned off since. Even the alarm service message comes on after the dashboard and electronics fail and then start working again.
Expert:  Eric replied 1 year ago.


The problem with changing the CEM yourself is that the immobilizer also goes thru it, which means that it will not start until you have it programmed, so you would have to have it towed to a dealership. And you will need to call your local Volvo dealer to see if they will. Many dealerships refuse to program customer supplied and installed control modules or even install customer supplied parts. This has to do with if the part is defective, most customers expect the shop to to do the labor to remove it for free and program the second one for free and get upset when they wont. Dealers just see it as one less potential headache to deal with.

And yes, you would have to go to a dealer to have it tested as it takes a VIDA scan tool, which is a factory level scan tool. and it requires a VIDA scan tool plus access to Volvo's tech site for the software to download into the new CEM.

Customer: replied 1 year ago.
I know I can't get away from the labor charge, and wouldn't want to, everyone deserves to eat. I just don't think I should spend the sort of money they would sell a new CEM for when I can get one from a salvaged vehicle.
Expert:  Eric replied 1 year ago.


They wont even attempt to program a used one as it wont take. These are vin specific and is write once for the vin programming into it, which means that you cant use a salvage unit.

Customer: replied 1 year ago.
I'm sure I can clear the EPROM so that it can take a new VIN.
Expert:  Eric replied 1 year ago.


I have no procedure for doing so, and volvo doesnt publish this since they state that you cannot do so. I dont know if you can do so with or without a VIDA scan tool, so it would be a chance you take if you elect to buy a used one.