Using a PIWIS 3 to diagnose a non-running 996

[Porschenstein]

Anyone have any advice on finding problems with the PIWIS? I'll post a link to a long thread on rennlist rather than going back through everything here.

The short of it is the fuel pump doesn't come on when trying to crank the car. Seems like the ECU isn't turning it on for some reason.
I say it that way since wiring, relay and ECU's ability to turn it on all seem fine, have also disconnected the fuel line at the filter to confirm no fuel when cranking.

ECU, Immobilizer and key set all confirmed good by ECU Doctors. I rented a PIWIS 3, I'm sure it's a clone but seems to work. I'll attach a few PIWIS results as well.

 

1999 C2 Coupe, DME 5.2.2

 

 

ServiceValuesReport.pdf

 

Sensors that can cause turn over but no start - Rennlist - Porsche Discussion Forums

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996 Forum - Sensors that can cause turn over but no start - I'm wondering if someone knows all sensors that must be functional for the stage 2 MPI & Ignition to come on when trying to start a 996. I've swapped the ignition switch electronics and Crank position sensor. I...

 

 

Edited March 6 by Porschenstein
add 1999 C2 Coupe, DME 5.2.2

[JFP in PA]

There are a variety of things that can prevent the fuel pump from running that will not throw any codes, including a blown fuse, a bad fuel pump relay, a bad pump itself, a wiring issue, and even the crank position sensor (the DME has a safety in it to prevent the pump from running if it doesn't see crankshaft rotation).

[Porschenstein]

Thanks, correct me if my thinking is incorrect on this but I think I can rule out any of the physical issues, meaning:

 

Jump the relay socket: pump runs

Tested the relay with cover off: contacts close with voltage (replaced it anyway, new FP relay now)

Connect with scan tool and tell the DME to run the pump: the pump runs

 

So I think it has to be a logical reason, meaning the DME isn't happy about something and isn't in a run ready state.

With no codes thrown, I'm hoping the PIWIS will give a clue from an actual value on the DME or Immobilizer, I have two that I'm currently concerned about.

One is on the Immobilizer I see:
Signal From Airbag: Not Present.

This one may be because it's a used SRS module, locked to another VIN, dealer says only a new one locked to your VIN will work, but does that shunt the fuel pump?

Some posts say they have used one from a donor but it would be good to know for sure if putting a donor SRS module could cause the no start.

I will also investigate the GR/OR wire going from SRS(24) to the Immobilizer(33) crash data. Not sure if that's the missing signal but maybe?

 

The other is on the DME:

Reference Mark Signal: Not Present (Is this the Crank Position Sensor?)

 

I did replace the Crank position sensor early on, I've made sure I didn't cross the connection with Cam sensor that shares the same mounting bracket.

If it is the missing signal, maybe it needs to be shimmed or something, I didn't see anything as far as shims on the old one that came out.

I don't really see the Tach needle bounce, but I have pulled spark plugs and watched them spark while the engine is turning over.

[JFP in PA]

If the tach is not bouncing when the engine is turning over, you have no crank position sensor signal at the DME......................

[Porschenstein]

Still looking for confirmation on a couple of things:

 

Can anyone say for sure that this is the Crank Position Sensor and it should have a "Ready or Present" value even when the car isn't running?

Is this definitive information that means we're not getting a signal from the Crank PS? 

 

Is this the crash data signal (GR/OR SRS pin 24 to I32 pin 33), I thought it always has a signal but the pulse changes if crash data is present.

Would this just throw an AB warning light or could this cause a DME no start since it's not getting the signal.

 

Thanks

[JFP in PA]

The "reference mark signal" is the crank position sensor in Porsche speak.....................

 

 

To precisely determine the crankshaft position, a reference mark signal is required.

Engine speed and reference mark are monitored via an inductive sensor. A larger gear notch in the ring gear (on the flywheel) serves as reference mark. The larger notch induces a higher voltage in the sensor.

A soft iron core partially bundles the magnetic field produced by the permanent magnet which then enters the space and closes again through the magnetically conductive parts of the engine. A steel toothed ring moving past the face of the sensor affects the magnetic field. The change in the magnetic field induces an electric charge that is used by the DME.

A fault code is stored in memory when no crankshaft position sensor signal is recognized within 60 crankshaft revolutions and the engine speed is above 500 rpm.

1 - Permanent magnet

2 - Sensor housing

3 - Engine case

4 - Soft iron core

5 - Inductor coil

6 - Reference mark

Could be the sensor connection, bad sensor, magnet has fallen out of the flywheel or even a bad DME (but not likely).

Test the sensor as follows:

Remove connector. Connect ohmmeter to sensor connector, pins 1 and 2.

Display at 20 °C: 0.8 - 1.0 k ohms

Connect ohmmeter to sensor connector, pins 1 and 3.

Display: 00 infinite ohms

[Porschenstein]

Thanks, I'll check it but it's brand new, connections were cleaned, so I'm thinking maybe wiring or the magnet.

Should it show "Ready or Present" even with the car not running?

 

Is this the Crank PS on DME pins 78 & 20?

 

 

[JFP in PA]

If the diagram is correct to the car, yes, and the DME should see it at all times.

[Porschenstein]

Thanks, yes it is the correct diagram just wasn't sure if Speed Sensor was the same as CrankPS... Also I forgot to say in the initial post it's a 1999 C2 Coupe, DME 5.2.2

[Porschenstein]

Not exactly bouncing, moves very slightly, opinions?

 

 

Edited March 7 by Porschenstein
shrink video

[JFP in PA]

I would be testing the CPS unit itself, and the wiring harness from the CPS to the DME for continuity and shorts.

[Porschenstein]

I checked the original CPS that I pulled out. Looks correct, makes sense because swapping it didn't fix it.

Display at 20 °C: 0.8 - 1.0 k ohms = 0.932, 0.930, 0.928, Seems to drop a bit with every check.

[JFP in PA]

What about the harness from the sensor to the DME?

[Porschenstein]

Unfortunately I'm working on the garage floor so I had to get it back up on stands and get to the CPS, not fun on your back...

The Uro Parts CPS I had in there shows .886. Before I checked the harness I just wanted to double check:

 

- Ohm test CPS connector pins 1-3 with DME connected to harness? (Looking to make sure pin 1 (signal) isn't shorted to ground since pin 3 is shield and goes to ground?)

 

- Should I also pull the DME connector and test CPS connecter pin 1 to x59/2 pin 9 and all the way to DME connector pin 78 and do the same for pins CPS 2-10-20 & 3 to WP4?

 

 

- Also, is that Weld Point 4 where all the shields come together, not Ground Point 4 right? Under the steering wheel area?

 

 

Edited March 8 by Porschenstein
Add additional image

[JFP in PA]

1.  We would never use the Unro part, they have proven to be unreliable.

 

2. Test the CPS by disconnecting it from the harness.

 

3. Check the harness isolated from the sensor, checking all three wires for continuity, resistance, short to ground; then reconnect the sensor and see if the pins at the DME read the same as the pins at the sensor.  We regularly see these cars with rodent and chaffing damage on circuits leading to the DME that cause all sorts of problems

[Porschenstein]

So nothing is tested with the DME connected to the harness?

 

Step 1 disconnect battery, wait a bit, disconnect DME?

 

I see now the CPS pin 3 shield I was wondering about should terminate at Ground Point 9, that sound correct?

 

Just working on my game plan before I play with it, I really appreciate you taking time responding.

[JFP in PA]

Look, diagnostics is all about isolating the problem(s) so they can be addressed.  With the sensor disconnected, you are only looking at the sensor, everything else is out of the equation.  Same thing when you disconnect the sensor and the connector at the DME, then you are only looking at the harness.  With the sensor connected to the harness, but the harness disconnected from the DME, you are looking at what the DME is seeing.  You need to go one step at a time, there are no short cuts.

 

Porsche tends to collect various grounds to specific ground points, mostly as a matter of convenience and reducing wire runs rather than running them all to one point.  All the cars have a multitude of grounding points in them as noted in the wiring diagrams. 

[Porschenstein]

Sorry if it sounded like I'm looking for a short cut, trust me I'm not, I've been trying to sort out what all is wrong with it since December of 2022.

The car on the tractor lift is my car... A lot of things were bad, it's been a long journey.

 

I was only trying to clarify that this test (Connect ohmmeter to sensor connector, pins 1 and 3 = 0 ohm) is done with DME unplugged from the harness.

 

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And clarify that I'm reading this correct and pin 3 terminates at GP 9.

 

Thanks again

 

[JFP in PA]

Correct, you run the same tests at the DME connector that you ran at the sensor, pins 78 and 20 at the DME connector should read the same as pin 1 and 2 at the sensor with the sensor connected to the harness: 0.8 to 1.0K ohms, which indicates the DME should be seeing the same thing you saw at the sensor.  Pins 78 and 20 should show no connection to ground and testing the harness from pin 1 at the sensor end to 78 at the DME end should not show high resistance, nor should pin 2 to pin 20.  If everything is good, it is not the CPS.

 

And the sensor ground eventually goes to GP#9 and should demonstrate continuity to ground at the sensor end of the harness pin 3 .

[Porschenstein]

✔️ Thanks

[Porschenstein]

I tested the CPS & it's connector back to the DME today. Seems like good news with a lot of possibly bad news and questions.

First, all of the CPS & CPS connector results seem fine:

 

Tested CPS pins 1-2 (.886), connected CPS to harness & tested X59/2 pins 9-10 (.886), tested DME pins 78-20 (.886) So CPS and wiring seem good.

0 Ohms on the wires from the DME to the CPS connector with CPS removed.

 

While checking CPS pin 3 I noticed I was getting tones in other places, since it's a ground it makes since that it would tone at other ground connections, but some seem bad. I also checked these results while connected to chassis ground rather than CPS pin 3, almost the same results.

 

While connected to CPS pin 3 testing continuity I received tones in all of these pins, as I said the ground ones make sense.

(X59/1 pins 23,24,25) (X59/2 pin 18) (DME pins 2,6,7,8,25,28,29,35,36,37,52,54,55,59,61) --> all toned back to CPS pin 3 Shield Ground.

 

While connected to chassis ground.

(X59/1 pins 23,24,25) (X59/2 pin 16,18,23,24,25) (DME pins 2,6,7,8,25,28,29,35,36,37,52,54,55,59,61) --> all toned back to Chassis Ground.

 

I'm thinking this might be normal on a lot of them since I can test / activate most of them via PIWIS or Durametric.

 

X59/1:

pin 23 - unknown but grounded

pin 24 - Start Lock / Starter

pin 25 - Start Lock / Starter

 

X59/2:

pin 16 - unknown but grounded

pin 18 - CPS pin 3

pin 23 - Throttle Valve Potentiometer

pin 24 - Idle Speed Positioner

pin 25 - Idle Speed Positioner

 

All of this on the DME connector tones back to chassis ground...

 

Edited March 9 by Porschenstein
Add additional info

[Porschenstein]

Was that TMI?... 

In post #1 I attached the Vehicle Analysis Log taken with the PIWIS III. I have only spotted these things as possible no start causes.

That's the CrankPS, Airbag Controller and voltage regulator/alternator.

 

DME
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*(Reference mark - signal not present) - wiring and CPS tested good.

*(Signal from airbag - not present) - wiring tested good

Immobilizer I32
---------------
*(Signal from airbag - not present) - determined this is normal with ignition on not running
                   
Cluster
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*(Signal, terminal 61 - not present) - determined this is normal with ignition on not running 

 

Anyone see something else of concern on the Vehicle Analysis Log?

 

Edited March 13 by Porschenstein
answer my own questions

[Porschenstein]

If the CPS signal is not seen but the CPS and wiring test good is it possible the TN-Signal coming back out on pin 80 is not making to the cluster and could cause the Reference Mark to be not seen? I'm assuming this wire feeds the tach.

 

Or maybe the timing ring is damaged? It was towed from Miami to Atlanta in first gear.

[JFP in PA]

What Neanderthal (1) Flat towed a Porsche anywhere, (2) Did so in gear? Jeeze.........

 

If you have tested the harness connector at the DME for the signal and it is good, you may have other issues: (1) the DME itself has an internal problem, (2) Ther may be a harness fault from the DME to the dash tach.  Fortunately, there is a way to test both: One of the pins (#9) in the OBD II plug is the same circuit that runs from the DME to the dash that you can test for signal:

 

[Porschenstein]

1 hour ago, JFP in PA said:

What Neanderthal (1) Flat towed a Porsche anywhere, (2) Did so in gear? Jeeze.........

A little harder to admit when you put it like that, but unfortunately the Neanderthal was me.

I drove down and picked it up from Copart. I think the tire straps held it tight though.