VX SS Digital Vs Analog speedo reading

[ozengines]

On my VX SS Ex-Chaser I have the normal speedo and also a digital speedo where the oddometer is. According to another web site the following text appears.

Any VT/VX/VY Commodore can have the "Police Mode" digital speed indication feature enabled under the Speedo dial with Tech 2 at a dealership. Takes about 3 minutes. In doing this, the vehicle looses the Speed Alert feature.

Do any of you other VX SS owners have the digital speedo activated as standard or is it actually a "Police Mode".
Inside my drivers door there is a yellow sticker that certifies the speedo accuracy as being tested. Would that have been for the dash speedo, the digital speedo or the Police radar setup ???

There is a 4km/h difference between my analog and the digital, which do I believe ?

[ozengines]

Any help on my question above ????????

[Ozzie]

the police have it specially activated.

all vt's and vx's have the option. to activate mine without a tech2 i need to hold down mode & set^ when i start th car.
only problem with it not being permenantly activated is that i have to do this step everytime if i want to use the feature.

by having it activated by a tech2 from holden, they are able to permanetly activate it.

[ozengines]

Thanks Ozzie, which do you think is the most accurate speedo, the big dail or the digital??

[fitz_vt]

well the LCD screen and the Big dial are fed by the same ECU........
so enevitbly they are the same reading your speedo needle must be out but if it has been checked for accuracy its been a cop car and maybe you should have it adjusted or checked have you put aftermarket rims on it??

[Ozzie]

Originally Posted by fitz_vt

well the LCD screen and the Big dial are fed by the same ECU........
so enevitbly they are the same reading your speedo needle must be out but if it has been checked for accuracy its been a cop car and maybe you should have it adjusted or checked have you put aftermarket rims on it??

yep exactly.

the digital speedo is the main reading. it gives out the reading to the analog speedo

[ozengines]

OK, thanks guys,
no original cop rims.
Will get it checked, don't want to get pinged by a radar.

[SlickHolden]

I just wish Holden would have all options in the trip, Instead of searching through buttons before you start.

[BLK-SAB]

You can go into Holden and get them to unlock this feature on your car. It over-rides your speed alert, as said, but who needs that if you've got a digital readout.


Had this done the day after i got my SS.

[235rwkw]

Originally Posted by fitz_vt

well the LCD screen and the Big dial are fed by the same ECU........
so enevitbly they are the same reading your speedo needle must be out but if it has been checked for accuracy its been a cop car and maybe you should have it adjusted or checked have you put aftermarket rims on it??

Not correct.

The PCM has direct input from the sensor and what it calculates is what is displayed on the digital readout directly to that readout. The analog on the dash is feed from the pcm via the BCM to the dash (which uses it own calculations based on pulses per minute ppm). The tech 2 can adjust the PPM to correct the analog gauge, and back when it was a cop car that probably what they adjusted. So the analog gauge would be more accurate, unless you have changed rims, diff ratio etc.

The problem being is using the Tech 2 to adjust PPM, this only adjust the dash analog gauge and not the PCM. More so a problem with gear ratio changes. the PCM still sees the uncorrected speed, so rev limiter and auto gear box changes are out as the pcm controls them based on what it sees. It will change gears at the wrong time, possibly over the limiter (depends what ratio you go to). Which means you could hit fuel cut on the limiter before it changes. but the dash will be right with PPM adjustment only, just the engine will not be right.

The best way to adjust the speed is via the PCM. Holden can't do that at dealers, if they can they are taking them to a tune shop. Tuning programs will adjust the PCM for tyre size, rim size and diff ratios in the pcm so it sees the right speed at the pcm. but for a cop car to be deadly accurate on the analog gauge they adjust it by tech 2, on a regularly checked dyno, as Oem they are about 5 kph out on purpose.

At one stage when i changed ratios the PCM indicated speed was 10% out to the dash when adjusted via tech 2 only many years ago. Currently my digital is 1 k out at 100k, the dash is 6 k’s under in comparison to the GPS unit.

analog reads OVER as per most oem dash analog readings, they do that on purpose as manufacturers are not allowed to read under, or everyone would be speeding. So At 100 KPH on a OEM dash you will really be doing about 95 kph, most ppl drive 5 kph over, so they are actually doing the right speed then 100 kph. But be warned 5 kph at 100 kph is not 5 kph difference at 60 kph, its a % factor.

Anyway to answer the posters question, run it on a dyno or use a GPS unit. With a gps you need to sit on the hwy at a consistent speed for accuracy. Then you will know which one is closer…

[fitz_vt]

Originally Posted by 235rwkw

Not correct.

The PCM has direct input from the sensor and what it calculates is what is displayed on the digital readout directly to that readout. The analog on the dash is feed from the pcm via the BCM to the dash (which uses it own calculations based on pulses per minute ppm). The tech 2 can adjust the PPM to correct the analog gauge, and back when it was a cop car that probably what they adjusted. So the analog gauge would be more accurate, unless you have changed rims, diff ratio etc.

basically what you have said i have somewhat made easier for others to understand, they are fed by the same damn sensor ok yes one goes through a BCM to interperate the data but essentially the same thing.....

[235rwkw]

Originally Posted by fitz_vt

basically what you have said i have somewhat made easier for others to understand, they are fed by the same damn sensor ok yes one goes through a BCM to interperate the data but essentially the same thing.....

sort of. same original data, but handled in by 2 separate calculations

one can be made to read 100 kph more than the other via adjustment of the calculations.

his question was which is the correct one. depends which one was played with. i explained why the readouts can vary, how to check which is right and how to adjust either.

Cop cars of this era usually had the PPK values adjusted to correct the speedo accuracy