Fix one thing , break another - P1875

[thebanjoman]

With larger tires on a 98 Sport comes an incorrect speedometer.  

My 'attempt' at recalibration,   I added a reduction box to the Speedo cable.  Now the MPH and Odometer reads very close to perfect.

If this was a Manual trans.. problem solved and done.  But it's not.

After adding the reduction box. Now I throw P1875 codes and eventually a check engine light.

Reason is..  VSS in gauge cluster and Speed sensor in 03-72LE  4 Sp Auto differ by more than 10km/h 


Per the 1800 supplementary service manual for the P1875 code.

DTC DETECTING CONDITION
While driving at higher than specified vehicle
and with more than specified throttle valve opening,
following conditions are satisfied for specified time.
. Vehicle speed sensed by vehicle speed sensor
speedometer) is more than 10 km/h lower than
sensed by transmission vehicle speed sensor when
4WD low switch is OFF, or
• Vehicle speed sensed by vehicle speed sensor (in
speedometer) is more than 10 km/h higher than that
sensed by transmission vehicle speed sensor when
4WD low switch is ON.


Any way of correcting this and keeping my reduction box in the speedo cable and stop the codes from being thrown?     i calculate the difference is now 14-16 km/h

With 40 years of driving under my belt I  would like a correct speedo and not have to do mph calcs in my head while driving or have another
external box to show my speed and  odometer.    I use the odometer for maintenance intervals.

Do I have any options?

[fixkick]

I am now editing this post, for truth and corrections and new questions.
1: 1998 sport. 4speed AT and 4wd. with new 2.3L engine.
2: the car has stock 1.8L ECU, right?
3; the car has stock 1.8L TCM , and if not you can not mix TCM TO ECU AND THE REVERSE BY YEARS NOr ENGINE SIZE OR COUNTRY , YOU DID NOT DID that , right"?
4: THE P1875 IS 100% UNIQUE ON THIS TCM AND we must not read the non sport books (G16) on TCM or ECU. for sure. and 1875 is speed error and not old transfer case switches bad, on all G16s

5: the cable must be speed up NOT reduced as you said tall tires now. slower drive shaft , what tires are they size. sure 10% larger circumference.

that is it so far..
but VSS1 must = VSS2 or the TCM and or ECU will not like that, the ECU does the P1 codes, P1 means factory custom DTC codes and we see now Suzuki changed the rules here on the sport.

[fixkick]

With larger tires on a 98 Sport comes an incorrect speedometer.  

My 'attempt' at recalibration,   I added a reduction box to the Speedo cable.  Now the MPH and Odometer reads very close to perfect.

If this was a Manual trans.. problem solved and done.  But it's not.

After adding the reduction box. Now I throw P1875 codes and eventually a check engine light.

Reason is..  VSS in gauge cluster and Speed sensor in 03-72LE  4 Sp Auto differ by more than 10km/h 


Per the 1800 supplementary service manual for the P1875 code.

DTC DETECTING CONDITION
While driving at higher than specified vehicle
and with more than specified throttle valve opening,
following conditions are satisfied for specified time.
. Vehicle speed sensed by vehicle speed sensor
speedometer) is more than 10 km/h lower than
sensed by transmission vehicle speed sensor when
4WD low switch is OFF, or
• Vehicle speed sensed by vehicle speed sensor (in
speedometer) is more than 10 km/h higher than that
sensed by transmission vehicle speed sensor when
4WD low switch is ON.


Any way of correcting this and keeping my reduction box in the speedo cable and stop the codes from being thrown?     i calculate the difference is now 14-16 km/h

With 40 years of driving under my belt I  would like a correct speedo and not have to do mph calcs in my head while driving or have another
external box to show my speed and  odometer.    I use the odometer for maintenance intervals.

Do I have any options?

The TCM and ECU both boxes in the dash both have VSS sensors. (VSS1 and VSS2)
the taller tires need, VSS1 cable to speed up 10%
the taller tires need VSS2, to speed up 10%'
or you get 1875. (only on sports do we get this code for vss errors

from your post here I see that the so called reduction box is not that, it speed up box.
but no tires told yet to me,
you didnt put those lowrider mexican tires on SPORT did you, I saw four of these folk drive off a cliff one day (death), when all 4 tires exploded at once with radial illegal
load ratings of tires wrong ( super low rated not for a 62 chevy)
why post lacking tires sizes, (load rating is your worry sure)

sure wish I knew all changes on the car, related to drive train (tires too) and ECU and TCM. etc.


the VSS1 is here, rear of box.

[thebanjoman]

With larger tires on a 98 Sport comes an incorrect speedometer.  (there is no such speedo for tall tires, at Suzuki.)

My 'attempt' at recalibration,   I added a reduction box to the Speedo cable.  Now the MPH and Odometer reads very close to perfect.

If this was a Manual trans.. problem solved and done.  But it's not.

After adding the reduction box. Now I throw P1875 codes and eventually a check engine light.

Reason is..  VSS in gauge cluster and Speed sensor in 03-72LE  4 Sp Auto differ by more than 10km/h 


Per the 1800 supplementary service manual for the P1875 code.

DTC DETECTING CONDITION
While driving at higher than specified vehicle
and with more than specified throttle valve opening,
following conditions are satisfied for specified time.
. Vehicle speed sensed by vehicle speed sensor
speedometer) is more than 10 km/h lower than
sensed by transmission vehicle speed sensor when
4WD low switch is OFF, or
• Vehicle speed sensed by vehicle speed sensor (in
speedometer) is more than 10 km/h higher than that
sensed by transmission vehicle speed sensor when
4WD low switch is ON.


Any way of correcting this and keeping my reduction box in the speedo cable and stop the codes from being thrown?     i calculate the difference is now 14-16 km/h

With 40 years of driving under my belt I  would like a correct speedo and not have to do mph calcs in my head while driving or have another
external box to show my speed and  odometer.    I use the odometer for maintenance intervals.

Do I have any options?

THE 1998 sUZUKI sPORT 1.8l j18 ENGINE CAR ,4DOORS, 4WD,  RIGHT? JLX SPORT,IS 4DOORS. 4SPEED AT.

ME: I can only guess what this custom car has now..
DIFFERENT 2.3L ECU
The TCM is still separate in all 3 years of SPORT
the TCM needs the VSS sensor at the rear of the AT4 box to read correctly and will not.
the ECU has the speedo, cluster VSS2.
this magic is so if the VSS2 dies, you can drive home and auto shift all 4 grears. if not for that , youd be stuck in 1st gear all the way home or in reverse. (that is what it does)
VSS1 IS PRIMARY , VSS2, IS SECONDARY BACK SPEED SENSOR, AND MUST WORK OR mpg,.. ODOMETER AND VSS2 WILL BE DEAD, OR IN THIS CASE READS SLOW.
THE CABLE MUST BE SPED UP NOT REDUCED BY 10%, TALL TIRES ARE TICKET GETTING TIRES,
AND BOTH SENSOR MUST READ THE SAME.
IS THAT CABLE BOX A CABLE GEAR SPEED UP OR DOWN ? IDK WHAT You have there good day.

Also suzuki changed the meaning of P1875 just for the SPORT, one more odd odd thing that.

It's actually a 2.3, not a 1.8 but in this application it's not relevant. I've put 5000 miles since the swap and love the extra power.

Once again you are 'dead on'.    I throw the code because of the difference between 'vss1' and 'vss2' is greater than 10Km/h.    

Given the speedo was cable driven the logical approach was to address it at the cable, not understanding that doing this would create another issue.

If the signal from 'vss2' at the trans could be adjusted the same amount that the cable adapter provides perhaps it would stop throwing the code.

It has been suggested to me that maybe a 'yellow box' that is used in electric speedometer applications could be used inline of 'vss2' at the transmission to bring the differences back under the 10km/h and stop the codes.   The speedo adjustment made was about 12% so maybe the output at 'vss2' could be adjusted to be 112% to compensate for the change.

It might be an exercise worth trying.

[fixkick]

what is this so called reduction box.
are these taller tires. or are the Lowrider, SHRINK tires, I can not see your tires, ok. why post lacking tire spec.? makes help near impossible,.

TALL tires as all 100% of all offroad drivers do, that do this change from stock, not lowrider tires, ever.
and for a fact reduction is wrong,
the cars rear drive shaft spins slower on tall tires.

2 cars. example
both car s are going GPU speed of exactly 60mph.side by side (true land speed)
the stock car shows 60mph, on the cluster, and in OBD2 scans
the 2nd car
has tall tires with 10% more circumference and the DRIVE shaft rear spins 10% slower
the cure is 10% faster speedo cable and lair box on VSS1 Hall sensor on the rear of the 4AT box.
the cure is a 10% cable speed up device not any reduction device. ever.
that is one cure.
and do know that that P1875 may take many driving cycles to set, do not drive around the block and expect it to tell you the truth. also look in OBD2 pending DTC codes.
P1875 on your car best I can tell is 100% different than other suzuki this year. G16 DTC code that is totally different caused. (transfer case switch errors on G16.)

[fixkick]

the sport TCM box has new DTC errors, for P1875, I did not know this sorry, SPORT cars are very rare. only seen one live.

[thebanjoman]

Holy Automotive Engineering Batman!!!!

I need to take time to read and digest the information you provided.     I have checked the 4Lo circuit end to end and it works according to the supplementary service manual.  I have removed for a test the reduction box in the cable so i feel confident that it is triggering the P1875 code because of the differences in sensors.    There have been NO other codes triggered.  

I'll see if i can call in some favors and see if I can a scope hooked up to see what I can gather to help me understand more.

It doesn't look like from what I am reading here is that using some form of 'off the shelf' box is not going to be possible.

Thank you for sharing. It is very helpful.

[thebanjoman]

Taking care of sick family members in and out of the hospital as well as sick pets I haven't had much time to look into this in greater detail.

I took the speedo cable reduction box off and have been driving the vehicle for a while with NO P1875 error codes being generated so it can be said to be confirmed that the reduction box, while correcting the speedo is in conflict with the VSS(2) on the Transmission.  The speedo reduction box is about 12% different to compensate for the tires, which is greater than the 10% difference the manual says the gauge cluster VSS and the transmission VSS can differ.

I wonder if I could count the pulses from the reed switch at the speedo and reduce them by 13% with a micro controller such as an arduino to again 'match up' the VSS1 and VSS2 sensors. 

Is it just one wire for the reed switch to the PCM ??  Trying to find this out (and color) in my FSM wiring diagram.

There are many examples of reading and generating pulses on the arduino but more research is in order. 

https://www.fixkick.com/sensors/tests/vss-testing.html  #6 tells me.

As you spin that port, the VSS opens and closes many times,  0ohms, infinity, zero ohms, infinity , over and over.  that is a good switch if in beep mode it beeps over and over.

If I could put an Arduino or other controller inline between the speedo and the PCM and count the pulses from the reed switch and generate the same amount minus 13% and send it back into the PCM I think it might work.  

Where am I going wrong?

[fixkick]

Taking care of sick family members in and out of the hospital as well as sick pets I haven't had much time to look into this in greater detail.

I took the speedo cable reduction box off and have been driving the vehicle for a while with NO P1875 error codes being generated so it can be said to be confirmed that the reduction box, while correcting the speedo is in conflict with the VSS(2) on the Transmission.  The speedo reduction box is about 12% different to compensate for the tires, which is greater than the 10% difference the manual says the gauge cluster VSS and the transmission VSS can differ.

I wonder if I could count the pulses from the reed switch at the speedo and reduce them by 13% with a micro controller such as an arduino to again 'match up' the VSS1 and VSS2 sensors. 

Is it just one wire for the reed switch to the PCM ??  Trying to find this out (and color) in my FSM wiring diagram.

There are many examples of reading and generating pulses on the arduino but more research is in order. 

https://www.fixkick.com/sensors/tests/vss-testing.html  #6 tells me.

As you spin that port, the VSS opens and closes many times,  0ohms, infinity, zero ohms, infinity , over and over.  that is a good switch if in beep mode it beeps over and over.

If I could put an Arduino or other controller inline between the speedo and the PCM and count the pulses from the reed switch and generate the same amount minus 13% and send it back into the PCM I think it might work.  

Where am I going wrong?

98 sport with 2.3L engine. stock ECU  stock TCM"


you are not going wrong
the Suzuki has 2 VSS, sensors, and they do not agree now. 
yes it is a reed switch in the speedo,, I have photos of all this, in the main page.  The reed switch no voltage refr. it  is only a switch. (makes it super simple to emulate)

the main cable, runs VSS2, in the head.
the rear of the tranny does VSS1. to the TCM, box.
both must be changed and the same way (RPM ) or it will set  DTC error, (conflicted, or as jeeps do, Incongruity.)

the speedo cable turns the speedo head, and that makes ODOM work and MPH and the VSS2 clicker work..


REDUCTION,  why that?    Big tires are speeding ticket getters. and reads slow.  
big tires have larger circumstance,  this makes the rear (drive) prop-shaft run slower not faster, and the MPH reads slow,and ODOM read less.
the axle I guess is 5.125:1 ratio, this is gear fixed, so as the end axles show down so does the front pinion gear and drive shaft
the speedo cable measure the rear drive shaft RPM (in any gear)
So any cable speed change box is speed up box. gear up, a  the cable cures 1 problem.  (unless thinking the cable turns the rear  wheel) relativity wrong.

the problem is there are 2 sensors. (my jeep has none it uses ABS sensors to do speed, all 4 and averaged, says jeep) so this shows the great variance on how this is done.
most cars have just 1,  the rear of tranny electric hall speed sensor.  (doing 2 things, shift points 4speed, and MPH ,etc) 
Not suzuki this is what makes the Suzuki so different.

yes and Arduino or any tiny micro can do this.  speed up.  10%   (at any given true speed, the tall tires, make the drive shaft run slower, 10% more circumference.
I do not have any 1998, ECU nor TCM schematics, so can not comment on wire colors.  to TCM.



the sport is not wired like any G16, nor do they share harnesses nor PCM really the Sport is and early GV< grand vitara, (beta version, LOL)

the PCM changed every year,  96, to 98 they changed alot, and the TCM did not change the 3 years, 1 P/N exists only.
your 2.3L i guess runs off a 1998 PCM/TCM right so only 98 PCM drawings match.

the sport did not move the TCM into the ECU in 1997 like G16 did. (and rename it PCM) this did not happen on the sport. (yes complex )

no.  and has a very odd setup the sport 1997,  where the ECU monitors the shifter and VSS2 and TCM monitors VSS1. VSS1 is a way more stable and accurate sensor to TCM)
and TCM is still in the dash all by itself, and they work as team in (96-98)
that means the TCM has its own, VSS, and the ECU has the other, in 1997
I have no drawings of the 1998. TCM nor PCM.
all sellers of TCM 38880-77e21 , sell it for 96 to 98 sport, so the words above about 97 are true. the master Suzuki shows 1 TCM for 3 years, and only one 1998 ECU  for USA.

each year has its own ECU. (and country)

and it does for sure have VSS1 inputs, to shift the box it does,  and IS WAY more accurate than that funky jumpy VSS2 in the speedo head.

the ECU VSS is yellow wire, and blue (or yell-red) 


VSS1 is seen her on the 4SP AT. ID #26

p/n 24791-57B00  id 26  this sensor goes to the TCM. for accurate shifting and accurate MPH speeds sent to the ECU.
if car is 4wd,  IS YOUR CAR 4WD?

the 4speed AT, has rear vss sensor, and the TCM sees 2 more switch sensors on top of the transfer case, these are 4wd yes/no binary logic and High.Low range logic,
so when in 4wd High the speed is 1:1 if in low the TCM sees the low range switch in low and does the math. ( a reduction of VSS speed at the LOW gear ratio)


not sure what you car has I will have to go back and read all ports, on this custom car.
sorry and next.

[fixkick]

I am still STUCK at tires SIZE why leave off such a very important fact.
endless tires made, endless rims, I can not at all guess what tires and rims are on this car ever.
and would be nice to know, for sure, at post 1 for sure.
virtual signature 1:
1998 sport, 4wd, 4AT, 4door, 2.3L new engine + UNKNOWN TIRES AND RIMS. (1.8L ECU and 1.8L TCM stock sill there)