Thursday, January 27, 2011

Crankshaft Position Sensor Replacement, 900's, 9000's, 9-3's, and 9-5's

Some issues have classic symptoms that throw up a red flag right away when a client is describing them. "The car wouldn't start after I shut it off for a few minutes, but would start right up if I let it sit for an hour" is classic Crankshaft Position Sensor failure.

This little sensor is mounted on the front of the engine on turbo SAABs from 1994 and up. It's job is to tell the engine management system the angle of the crankshaft. Essentially, it's just a magnet that corresponds a pulse from a trigger wheel mounted on the crankshaft. However, without the signal, the car doesn't know what order to ignite spark or fire the fuel injectors, therefore leading to a no start condition.

Sometimes the sensors just fail and have no visual signs of wear, but on the car I was working on today, this was not the case.


Old, broken wiring harness vs. new sensor.


Oil from an oil leak at the cylinder headgasket soaked the sensor harness, causing the rubber to swell and eventually rupture. Heat from the turbocharger also aids in the degradation, though there is a metal heat shield over the sensor to prevent this. If this was a clients car, I would have definitely caught it in the consultation, but this was an out of state tow in that broke down locally and had the car towed to me.


Where the sensor mounts, if you look hard inside the hole you can see the trigger wheel the sensor reads its signal off of.


Easy enough job to do. A common failure that can leave you stuck and stranded... no bueno.

I'm getting out of the cold and heading to Florida for a week on a bit of a vacation. Heading to the Rolex 24hrs of Daytona race on Saturday/Sunday. See "Yinz" later.

2 comments:

RICARDO BARTHE said...

Chad: I like a lot your webpage. I´m writing from Madrid-Spain- and I am completely desperate because I have changed twice the CPS, after 2 months and I still have the same problem. The computer says again CPS error, could any part of the engine damage the CPS sensor? Is there any way to remove it and start the engine? I do apologize for my English level.

Jeff Roble said...

Sensors are transforming the way engineers think about position sensing

Distance Sensor