XC90 SRS Service URGENT message

[aslan]

Originally Posted by SwissXC90

Disconnect battery, wait 30min, then disconnect each front crash sensor (under the headlamp assembly) and check the connectors are clean and fit with sufficient friction.
If in doubt clean with contact cleaner spray

Thanks SwissXC90. I have done the above over the weekend. Cleaned the connectors at the sensor and also at the connector where the sensor harness joins to the main harness. Both sides.

I will test the sensors as advised and report back.

If they are defective, and as they are a simple device, would I fine replacing them with a used good sensor? That is by checking the used sensor first with a multimeter.

[SwissXC90]

Originally Posted by aslan

Thanks SwissXC90. I have done the above over the weekend. Cleaned the connectors at the sensor and also at the connector where the sensor harness joins to the main harness. Both sides.

I will test the sensors as advised and report back.

If they are defective, and as they are a simple device, would I fine replacing them with a used good sensor? That is by checking the used sensor first with a multimeter.

Yes, the sensors are very simple.
You can replace a faulty sensor with a good second-hand used one, or with a good brand new one.

If you have already replaced the sensor, then it would be a good idea to check wiring loom integrity. Use the wiring diagram and a multimeter, check each wire from sensor back to SAS control unit (disconnect battery etc to do this)

Always use VIDA to help you in the diagnosis here

[aslan]

An update. The old sensors resistance was around 140-150 for both sides.

I 'borrowed' another used front impact sensors. Different part number but it appears the same thing as my current sensors' part number supersedes the 'borrowed' used ones. I measured the 'borrowed' ones and both measures around 99-101.

Anyhow as both sensors were registering similar resistance I installed the used sensors. SRS warning still came up. Cleared it and read again the DTCs. Am still getting the same fault - no communication with front sensors.

This doesn't sound good. I think the used sensors are fine and if they are not compatible with my year model, I thought I'd assume a fault saying wrong signal or wrong configuration (these do exist in VIDA)

I am able to assess the SRS module. Only info I could test was that the SRS module was receiving voltage. Looking at the wiring diagram the front L and R connects to the SRS module using two different wires. Pretty odd to have both wires broken or damaged when the car hasn't been in any accident.

Do I have a faulty SRS module?

[SwissXC90]

If I was you, I would exhaustively test the sensors and cabling and clean every possible source of dirt and corrosion from every connector involved between SRS module and sensor before making the leap of having the SRS module repaired or replaced.

You need to also measure the resistance at the SRS module connector, not just on the sensor.

You haven't told us what year XC90, so I will now assume it is a 2005 XC90
From the 2005 wiring diagram, the following sensors...
7/115 Left-hand front side impact sensor
7/116 Right-hand front side impact sensor
...both connect with 2 wires each back to the 4/9 Control module, Supplemental Restraint System


So you need to check for integrity of each wire, ensuring that each wire is properly isolated from the chassis (use an ohmeter)

If you have verified the sensors and the cabling are OK, as per the wiring diagram applicable to your model year, and you are convinced that your results are correct, then the only remaining component in the system is the SRS module.

[SwissXC90]

OK so assuming a MY2009 XC90 (I have the same car) then here's the data from the MY2009 wiring diagram:

The front impact sensors are devices 7/178 and 7/179

7/178 Front impact sensor, right
7/179 Front impact sensor, left

Both are wired with 2 wires back to the SRS module
Neither wire is connected to ground, neither wire is connected to power

The wires go through 2 connectors:
Right: 54/122 (week 20-21) to 54/3.1
Left: 54/113 (week 20-21) to 54/3.1

I read the above to indicate that only cars made in week 20-21 have connectors 54/122 and 54/113

54/3.1 is a 36-pin gray connector connecting the engine harness to the passenger compartment harness and is located on the firewall or inside the passenger compartment under the dashboard area

The 4/9 Supplemental Restraint System module (SRS) is located in the center console to the rear of the gear lever
You must measure wires at the SRS module to verify wiring integrity