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-   -   Running cluster outside of car - mileage stuck? (http://www.saturnfans.com/forums/showthread.php?t=237862)

jpsuli 08-12-2019 08:49 PM

Running cluster outside of car - mileage stuck?
 
1 Attachment(s)
Hello,

I have a 99 cluster that I want to run outside of the car, I found this:
[QUOTE=OldNuc;2225062]5000pulses/mile from the PCM. Below from FSM.

SPEEDOMETER/ODOMETER
The speedometer receives vehicle speed information from the Powertrain Control Module (PCM ). The vehicle speed signal is passed through an RC filter to the input of the speedometer/odometer driver Integrated Circuit (IC ), located in the instrument panel cluster. The high-to-low edge of the square wave input triggers the IC to provide a well defined pulse of current to the coil of the speedometer gage. The IC also counts the input transitions and uses this information to drive the odometers. The vehicle completes one mile for every 5000 pulses received from the PCM.

There are two odometers in the instrument panel cluster. The odometer shows total mileage since the vehicle was built and cannot be reset. The trip odometer which shows total mileage since last reset, and can be reset to zero at any time. The two odometers are not synchronized. This means that even through one of the odometers may advance by a mile/kilometer the other one may or may not advance to the next mile/kilometer at the same time. The odometer is back lit by a single bulb to make it easier to read in all lighting conditions.

TACHOMETER
The tachometer is directly controlled by the powertrain control module (PCM) using a Pulse Width Modulated (PWM ) signal based on the signal received from the Crankshaft Position (CKP ) sensor. The PWM signal to the cluster is passed through an RC filter and sent to the tachometer driver integrated circuit (IC). The high-to-low edge of the PWM signal triggers the IC to provide a well defined pulse of current to the coil of the tachometer. The engine completes one revolution for every six pulses received from the PCM. The PCM monitors circuit 121 for an open, short to ground or short to voltage and will set DTC P1693 if certain parameters are met.[/QUOTE]

I grabbed a PWM switch and found the two wires that control ignition and the speedo, I was able to get it to work somewhat unreliably though the mileage does not move.

Any thought to get the mileage to work? I have spare PCMs to make it work, will try to play with it this weekend.

fetchitfido 08-13-2019 09:54 AM

Re: Running cluster outside of car - mileage stuck?
 
3 Attachment(s)
Going by the diagram the Speedometer/Odometer just needs power, ground and signal to work. Ground & signal pins are on a different connector from the power pin.
The description of the signal required sounds pretty picky, if the square wave isn't 0-12v and a true square it won't work properly.

jpsuli 08-14-2019 12:37 AM

Re: Running cluster outside of car - mileage stuck?
 
[QUOTE=fetchitfido;2304701]Going by the diagram the Speedometer/Odometer just needs power, ground and signal to work. Ground & signal pins are on a different connector from the power pin.
The description of the signal required sounds pretty picky, if the square wave isn't 0-12v and a true square it won't work properly.[/QUOTE]

Wow, these diagrams are really helpful! The wiki didn't go into such specifics. I appreciate you finding them for me.

So maybe my PWM switch provides a far too dirty signal for the cluster to properly register the movement as actual mileage. I will play around with my raspberry pi to define the actual pulses sent to the cluster.


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