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Discussion Starter · #1 · (Edited)
I replaced the engine speed sensor (also called the RPM sensor, G28) on my '99 AEG engine today. Here are my recommendations on replacing an engine speed sensor.

First, the symptom of a bad sensor is sudden stalling with no check engine light or DTCs set. The car will usually restart again as if nothing had happened. I had the engine cut out on the highway one time where it suddenly shut off. There were no unusual noises or vibration, just complete power loss. A couple of seconds later the engine started up again, instantly as if nothing had happened. The car slowed from 60 to 55 or so while the engine was off. With my manual transmission the engine was still turning plenty of rpm's when the engine came on again. Traveling at slower speeds or with an automatic transmission the engine may not restart itself and will stall out. When I got home I hooked up the car to VCDS and there were no trouble codes for the engine.

1. It is difficult to see the sensor tucked in above and to the right of the oil filter. It can be removed working from above. I removed the oil filter (I was changing the oil anyway) and the oil cooler. I highly recommend removing the oil cooler as it allows you to actually see the sensor, however you will have to drain the coolant and disconnect the coolant hoses to the cooler to do it. It will give you a chance to replace the gasket between the oil cooler and its mounting flange. This is common source of an oil leak and probably should be replaced periodically anyway. After looking at what mine was like I'd say it should be replaced whenever the coolant is changed.

2. A 1-1/16" socket worked perfectly to remove the nut that holds the oil cooler on. The metric size would be 27 mm. The torque when replacing the nut is 18 ft-lb.

3. My car doesn't have a secondary air pump. If you have one it may need to be removed for access, I'm not sure.

4. The sensor is held to the block with a single 10 mm head bolt. A socket and 6" extension make removal simple. The sensor itself needed a little force to be pulled out of the block. I grabbed it with pliers to twist and pull it out of the opening.

5. The connector is near the dipstick funnel. There is a tab on the side of the connector that must be pressed in and pulled back to release the connector. The sensor side of the connector slides into a slot in a bracket on the engine. It fits in tightly. I had to pry it up from below to get it to slide out of the bracket.

6. There is a cable guide pressed into a hole in the engine block. Just pry it out of the hole in the block and then move it to the new sensor.

7. When I tried to start the car for the first time with the new sensor it took 3 or 4 tries on the starter before it would run. Apparently the ECU needed to learn the new sensor. It has been starting reliably since then.

Overall, it is not too hard to do if you just plan on draining the coolant and removing the oil cooler.

Update: The intermittent no-start didn't go away and I found out the replacement sensor was bad. The engine wouldn't start at all with the next sensor. The third one was a Bosch and it has been working properly. So, if you have a no-start condition and replacing the engine speed sensor doesn't fix it, don't assume that you have eliminated the speed sensor as the cause!

Also, after putting in two bad sensors, replacing the original twice and finally putting in the good one in, I've gotten so that I can replace the sensor in 15 minutes without removing anything (again, no SAI pump). The harder part is putting the cable back in its original routing. So, it can be done without removing anything if you know where everything is.

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Just for records sake, I have a Secondary Air Injector Pump (SAI) and had to move it out of the way for easy access.

BTW, if you go to AutoZone and get your beetle scanned, and the readout says "CKP, crank position sensor" it's the same thing as the "Engine Speed Sensor".
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