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Porsche 993: Why Won't My Car Start?

Even the Porsche 993, one of the most venerated cars in Porsche's history, isn't exempt from having an issue here or there. So what do you do if your prized P-car won't start? Read on to find out.

By Nik Romano - April 7, 2015

This article applies to the Porsche 993 (1993-1998).

A no-start condition can be extremely frustrating and inconvenient, especially for those who rely on their Porsche 993 for daily driving duty. Frequently, the root cause is electrical as there are many circuits and systems that must be activated in order for a car to start. If just one small component fails, you are out of luck. A simple low battery can be easy to diagnose, but what if the battery is fine and the car just won't start anyway? The situations listed below assume that you have a known good battery, with tight connections.

Materials Needed

  • Multimeter
  • Lug wrench
  • Jack and jack stands
  • Wrench and socket sets, including hex sockets

Situation 1 – Utter silence

One of the best ways to tell what is wrong with your car, or to at least point you in the right direction, is to listen to what sounds the car makes while trying to crank. If turning the key has no effect whatsoever – the starter doesn't move, and doesn't even click – then the problem almost certainly lies somewhere in the wiring leading up to the starter.

Grab a friend and check for voltage right at the starter while they are cranking. If you see no voltage, the problem lies farther up stream. Test for voltage at every connection as it leads back to the fuse/relay block, the ignition switch, the clutch interlock switch, etc., all the way back to the battery. Eventually, you will find voltage. The problem will lie somewhere between where you have voltage and where you don't. It's crucial to have and understand a wiring diagram to do this properly, otherwise you might end up measuring the wrong things and never find the problem.

If you do have voltage at the starter, then your solenoid has gone bad, and the starter unit needs to be replaced.

Figure 1. Always have your wiring diagrams handy.

Situation 2 – Clicking but not cranking

If you turn the key and hear a distinct click from the back of the car, the diagnosis is pretty easy. The click is the sound of the solenoid activating, which lines up the starter gear to the flywheel in order for the starter motor to work. Usually you can't hear it over the sound of the motor cranking, but if the motor has gone bad, the click will be the only thing you hear. Replace the starter, and the car should be back to normal.

Figure 2. The starter motor is at the top of the transmission, passenger side. You will need to remove the axle to replace it.

Situation 3 – Cranking but not starting

The starter motor cranks the engine, but it wont fire up. There is a common issue in 993s where what is known as the "DME Relay" goes bad. The starter motor works fine, but the ECU won't give the engine the signals it needs for fuel and spark. Try replacing the relay with a known good one.

Another possibility is that the immobilizer is being triggered. 993 key fobs have a wireless transmitter that speaks to a receiver in the car. If they become out of sync with each other, the car won't start. Having the fob re-learn itself to the car can fix this problem.

Figure 3. Part of the immobilizer system is inside the key fob.

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