matty8

Hi, I'm looking for some advice as I've come to a dead end using up all the info gained from other threads out there.

My recently purchased 996 tiptronic (which has been standing for most of the last 10 years) is starting about 50% of the time, the rest of the time there is no crank, everything appears normal, just no crank! It may start in 10 minutes or 10 hours, but will start again at some point. It's pretty random, the only continuity is that if it has been running for a while after I leave it for a minute or two it wont start (no crank). Error code 5284 (electrical connection between TC and DME) is present when the non starting fault is present and not when its starting ok - this is all I have to go on now but don't know what to try. Maybe there's another ground lead I could test?
What else I know -
Its not the battery - new one measuring 13v, not exact spec but slightly higher Amp hours.
Its not the starter - bridging the relay will make it start
Its not the relay - have swapped them about, but when the problem exists there is less than a volt going to the relay, else full voltage
Don't think its the ground lead - engine casing measures full voltage, have cleaned the chassis end but not the casing end
Not the ignition switch - replaced that
Don't think its the tiptronic selector not being in park - its displayed on the instrument cluster
Don't think its the immobiliser - no error code and alarm light on dash goes off when key is turned in ignition after manual locking

Any knowledgeable advice gratefully received TIA

DBJoe996

Crank Position Sensor...maybe

matty8

...but it doesn't crank at all or starts and runs fine, so don't think I need to investigate this?

DBJoe996

Actually sounds like the ignition switch. What did you replace the ignition switch with? Brand...source..

matty8

'Meyle' from Amazon, not 'genuine Porsche' but unlikely that it would have the identical intermittent problem to the one it replaced

jumpy chunky

May help to know the year model of your 911.

Have you checked to see if the car turns over while in neutral?

matty8

It's a '99 car. Changing from Drive to Neutral makes no difference as to whether it starts or not.

hardtailer

Brake light switch, maybe? Assuming you need to apply the brakes for the starter motor to even engage.

matty8

No, no brake application required unfortunately.

My main focus is the 5284 error code - not sure how it's linked to the car not turning over

Porschetech3

Code 5284 is a communication error between the engine control unit and the transmission control unit..

The engine control unit will not allow the car to start unless it gets a communication from the transmission control unit telling that the transmission is in park/neutral and starting is safe/OK..

High and Low CAN wires in the trans conector are pin 85 and 86..

I would replace/rebuild the two CAN wires from DME to TCU and see if that fixes the intermittent issue, if not a new TCU may be in order..I have had to replace a few TCU's due to no start and sometimes the selector LED's will flash when the fault occurs

matty8

Excellent! Thanks Porschtech3, makes sense - I was stumped as I thought TC was for traction control. The error code showed up under the ABS check. This means I can make some progress, I'll check out the wires and connections - do you know which pins they connect to in the DME?

168Sierra

I believe it is pins 85 & 85 on the DME also.
See section L184, L185 on the attached wiring diagram

matty8

This is the error that I came up with from my Google search - definitely listed as an ABS / Traction control Issue? Or is there something I'm not understanding?

matty8

also..... had a thought. When I picked up the car I had to jump start it at a service station in a bit of a panic - just hooked it up to the battery - could this have fried the ECU?

and..... The TC indicator light on the button is illuminated when I switch the ignition on - is this normal?

hardtailer

No, jump startimg as described hasn't fried the ecu.

Illuminated upon ignition on but should extinguish after a couple of seconds.
If it lights up after having reached a speed of 4-5mph there is a wheel speed sensor related problem and the ABS Amber light should appear too.