Volvo S80 2.9 ... does not start

Autavia · Post by **Autavia** » 15 Apr 2025, 14:37

Hi everyone
I have an S80 2.9 without a turbo. From one day to the next, it wouldn't start, never had any problems before. First, we checked the fuel pump, which is fine. The ignition is OK, but it turns over, but it won't start. Then the scan came up with an error code P0335, meaning crankshaft position sensor. We've replaced it, but it still won't start. Another scan, again with the same error code! The crankshaft position sensor is new! We checked the cables from the sensor to the control unit, everything's fine! My mechanic thinks it's the control unit...! If the control unit needs replacing, the ignition key needs to be reprogrammed. I read that this isn't possible with a used control unit, only with a new one, which is supposed to be very expensive. What do you think, does anyone have a similar problem...?

Vova585 · Post by **Vova585** » 15 Apr 2025, 19:46

1. Was the sensor brand new OE/OEM or from ebay, Amazon, advance..? If you not sure about quality of the sensor-better replace with used one from salvage yard or brand new Oe from reputable source.
2. Make sure the mounting place is clean from any rust,debris and sensor is installed correctly.
3. Inspect carefully wiring to the sensor. Look under rubber protector cap of plug to the sensor. Look around the harness if there is no exposed wire that can short to ground.
4. Before calling ecm I would make sure that signal is getting to it when the car is not starting. For that you will need to invest time to research what system your car uses is it Hall effect(3 wire sensor) vs variable reluctance(2 wire). Based on quick glance part search it is 2 wire sensor. If so, compare resistance of new sensor to old.
5. Invest Into small 1-2 Chanelle oscilloscope and check the signal at ecu(I would use gentle backprobing with t-pin needles or buy online small needle attachment to backprobe.
6. You can always send your ecu for repair instead of trying to buy new. Xemodex might help to test/repair(not cheap).
7. Sucks to deal with intermittent issue. If possible might try dealer level diagnostic woth specific question. Hey i have such and such code. I replaced my sensor with quality part it does it again. Help me determine where is the problem harness vs ecu.
Good luck.

Autavia · Post by **Autavia** » 16 Apr 2025, 09:59

Hi there
I will do that, thank you for the advice in advance!

pranayama · Post by **pranayama** » 06 Nov 2025, 18:03

Disconnect the battery first for like 20 minutes and see.

If not, try disconnect overnight and see.

Also, try shorting the positive and negative battery cable when disconnected before connecting to the battery. This should be the CEM reset procedure or similar.

One way is also disconnect all the fuses in the engine and the driver side and see as well.

This car is known for electrical or wiring issues.

ophelie123 · Post by **ophelie123** » 03 Dec 2025, 05:47

P0335 that comes back even after replacing the crankshaft sensor usually means the ECU isn’t reading the signal at all. Before assuming the control unit is dead, there are a few things to check:

Check the reluctor ring (tone wheel) on the crankshaft. If it’s cracked, loose or dirty, the sensor can’t read it even if the sensor is new. This is a very common cause.