• A Plus Truck Repair

Volvo 2010 failed speed sensor SPN 84 FMI 19 SPN 84 FMI 9

Updated: Mar 5, 2019

I had a Service Road Call regarding Volvo semi truck 2010 not getting up to speed passed 35 mph, Cruise Control stopped working, Speedometer not working and J-Brake is nonoperational. Thanks to the Driver he was able to pull the fault codes up on a Volvo Dash by internal Vehicle Diagnostics System and the codes were: SPN 84 FMI 9 and SPN 84 FMI 19 both related to VSS (Vehicle Speed Sensor), which is located right behind the tail part of transmission to the side of the output shaft. I have verified the fault codes on dash and even without checking their interpretation with my truthful Bosch ESI 100 KTS Truck diagnostic tool. I went under the truck to check the VSS sensor. Have checked the wiring and connector and all seemed to be looking OK: no signs of chaffed wires or corrosion on contacts were evident. I also checked the output shaft for excessive radial play and presence of some metal particles stuck to the sensor housing - nothing concerning was found there either. I went ahead and proceeded with my Lock out Tag out procedure and went under the truck again with some tools for removal of faulty sensor. And it was stuck in there pretty bad due to plastic sensor housing bing placed in the metal casing! I have tried "liquid wrench" and soaked the sensor all up in that and left it sitting for a good 5 minutes, tried to rotate it after that, but nothing worked. I then used a "brake fluid" and applied it to under the sensor and above it hoping to get it in between the sensor and the metal housing, let the brake fluid to penetrate the sensor surroundings and tried with china lock pliers to wiggle it. Finally the top piece where the connector is gave out, leaving the bottom (plastic) part still inside housing. I have read on one of the forums (link below) that truck got towed to a dealership for sensor to be drilled out of it's housing. Unless they were talking about sensor holding M8 bolt the sensor can be removed without any drilling involved: as I mentioned above housing of VSS sensor is made out of plastic. By inserting about 12-15" pry bar between the output shaft and plastic sensor housing I was able to finally pry the remainder of a VSS out. After cleaning the opening of a sensor with metal round wire brush and blowing off the debris and rusty dust with compressed air and purchasing the new part (which was about $40) I have installed a new sensor in and reconnected the wiring. After I went inside the cab and connected my Bosch ESI 100 and cleared already "inactive" codes. They all cleared out and all the non-functioning components resumed their functionality. Things to consider for doing such repair: brake fluid for loosing the stubborn sensor, try working the top portion of sensor out first. Check the resistance value: the old faulty sensor measured 575 kOhms, whilst the new one was at 3.2 kOhms. This sensor has a very simple design: inductive pick up coil, sending the analog signals to VECU (Vehicle Electronic Control Unit), where it gets analyzed and converted into "digital interpretation" of a sine wave. In other words by the speed of frequency of changing of a sine wave the VECU determines the speed of output shaft, thus making a decision about the speed of a truck. All and all I hope this article will help you guys in your mobile truck repair business if you encounter the same conditions during your road call.

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