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Fix one thing , break another - P1875
#1
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?
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#2
ill go mum  here. (no custom cures by me)
j18 are a pain, out guessing OBD2 DTC reasons.
but you can only fix the low RPM on the tail shaft 2 ways, and is 2 sensors, the crude one in the cluster and the accurate one on the tail shaft. (vss tranny rear, sensor)
you did one, (speedo cable gears)
now the other awaits.
and yes, hi/low switch most work and not bounce driving,
http://www.fixkick.com
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#3
(12-12-2019, 12:44 PM)fixkick Wrote:
(12-12-2019, 11:00 AM)thebanjoman Wrote: 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 1998 sUZUKI sPORT 1.8l j18 ENGINE CAR ,4DOORS, 4WD,  RIGHT?
the car with 4wd has speedo cable on the transfer case. end. (best I know so far, like G16)

the 4speed box also has a VSS sensor.  so there are 2 sensors to deal with. (cluster Vss cable and 4speed box vss sensors)

the books on thAT are not that clear,  but 1 sensor is primary, the box sensors VSS1
and the speedo head is vss2, the backup sensor. (The cluster sensor is sloppy with cable drive so is backup)

how the TCM (inside the PCM) decides which one to use under failures I do not know. 

the 4speed transmissions uses VSS1 for more exact shifting, and to detect, clutch pack slips etc.. and errors for that into matching DTC.'s

the tall tires, make the 4speed box Vss1 sensor read wrong.   the cable fix only fixes cluster speed.


my new jeep uses ABS sensors (x4) to measure speed (MT box), and we have to reprogram the PCM to make that correction. for tall tires.
Tire changes are a pain, now. for sure with any electronic shifted transmission.

the VSS 2 is so you can auto shift 4 gears if VSS1 dies.  not a bad deal there, but sure calibration is more hard.

[Image: mECoa2y.jpg]
http://www.fixkick.com
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#4
(12-12-2019, 12:44 PM)fixkick Wrote:
(12-12-2019, 11:00 AM)thebanjoman Wrote: 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 1998 sUZUKI sPORT 1.8l j18 ENGINE CAR ,4DOORS, 4WD,  RIGHT?
the car with 4wd has speedo cable on the transfer case. end. (best I know so far, like G16)

the 4speed box also has a VSS sensor.  so there are 2 sensors to deal with. (cluster Vss cable and 4speed box vss sensors)

the books on thAT are not that clear,  but 1 sensor is primary, the box sensors VSS1
and the speedo head is vss2, the backup sensor. (The cluster sensor is sloppy with cable drive so is backup)

how the TCM (inside the PCM) decides which one to use under failures I do not know. 

the 4speed transmissions uses VSS1 for more exact shifting, and to detect, clutch pack slips etc.. and errors for that into matching DTC.'s

the tall tires, make the 4speed box Vss1 sensor read wrong.   the cable fix only fixes cluster speed.


my new jeep uses ABS sensors (x4) to measure speed (MT box), and we have to reprogram the PCM to make that correction. for tall tires.
Tire changes are a pain, now. for sure with any electronic shifted transmission.

the VSS 2 is so you can auto shift 4 gears if VSS1 dies.  not a bad deal there, but sure calibration is more hard.

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.
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#5
yes both VSS1 and VSS2 both can in fact be scaled, (gears on 1cable) but only electronics can with VSS2, (no withstanding , Rube Goldberg cures LOL)
this  drawing is 97 sport. very close or same. 2 wire sensor proofs. (non HALL) off my tranny page.
https://fixkick.com/tranny/automatic-slu...CM-4sp.jpg

VSS2  is coil sensor 2 wire and not a 3 or 4 wire hall sensor sadly, that means the cable is shielded and is very tiny signal, with weak 1volt pulses, sinusoidal shaped,
The only way to work this type of signal as did suzuki TCM is using a Zero crossing detector ZCD.  effectively making it HALL(like) sensor like but inside the TCM.
producing a clean square wave, for RPM. on the ZCD output pin.
One can do that using only 2 ways,  (analog way is no good, IMO)so 1 way.

VSS2 _ (2)  to ZCD>>>>cpu i/o input,  >>>>> truth table look up>>>> then send outputs pulses to output pin 10% higher RPM (HZ). using the stepper motor way? PWM inside the Arduino?
10% assumes new tires is 10% larger circumference.

this is not a perhaps thing,  you can in fact lie to any CPM made, or any computer, if the lie is perfect it can not detect any errors. and will work. for sure.

the one exception, is a too smart PCM say in 4th gear when box ratio is 1:1. the then engine RPM is same as VSS2 , if the PCM sees that as and error it will fail. (2 ways)
The PCM or more accurately the TCM internal brain now, (moved in 1997) DOES IN FACT CHECK FOR TRANS missing clutch pack slip. not just like you saw, SPEED is wrong.(low)
but that is RPM drop illegal. per gear.  and is pack slip, end of life for one transmission, bad clutches.
On a stock car with stock tires read drive shaft RPM too low is clutch pack slip,.  the TCM knows at all times the gear selected and TCC lockup state) and will warn of that (DTC)

but in your case you are only correcting the error to normal so there is no error, at all. (a re-scaling the RPM)

yes this would work, it is not theory, it will work. (IMO)

way 2 , and will be very hard to do is analog way,
Freq, to voltage converter.

VSS , ZCD >>>  VF , then >>> 110% amp, 10% gain amp analog >>> VF (reverse conv) to PCM (VSS)
the problem is the errors will be large at low RPM .

way3  is DSP,  OVERKILL here,  DSP are not cheap but are amazing, I have DSP based, PSU here (computer) and DSP, RADIO (ham) called a "SDR" software defined radio.
the DSP ,digital signal processor , can do this but is now cheap or easy to do.

way 4 (rube Goldberg way)
gear box, yah again, steps up RPM 10% and hall sensor input. but no way to connect new gears to that old TRANNY.
gear shaft main>>> new VSS shaft and mech fit, to gears, 10% higher, RPM, then to HALL then to PCM.



the old codes 1996, conversion tcm.
https://fixkick.com/CEL/4-spd_TCM%20codes.jpg

1875 is Esteem code.> ours is 4wd switch error, the codes must match the PCM used, and year,  not sure what PCM you run. (sorry if I forgot)

Px875  the x means factory code, and each car and each maker decides what to use 1875 for.
In this case its ESTEEM?
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#6
vss codes are p0500,,all P07xx codes are TCM

then come P1, factory only codes. only suzuki codes work here, (rule1 of OBD2 is that)

the P1 codes all are here.
https://geo.pink/download/145

Im and not sure what PCM you have, 98 sport or Esteem? sorry.
the 4wd switch Hi/lo will also kill dead ABS. if wrong. hi/lo switch bad is not good.
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#7
03-72LE VSS has no gear on end, and with no gear, means suzuki does not sell gear sets for all the axles run world wide. the cable vss has gear sets sold by suzuki, in plastic gears.
also, if the Hi/low switch fails, the VSS signals are now useless, not knowing transfer case ratio is impossible for the TCM to know what to do.
In effect there are 3 speed sensors, engine RPM tranny/clutch input RPM and 4speed out RPM, and transfer case output RPM (VSS) (on modern cars up to 5 sensors here)
The Hi/low switch must work and yours does not .

so if 1875 fails, fix the hi/low switch first, never any other VSS error of any kind (last)

best I can tell lacking a full 1998 FSM, Ive never seen one, and are rare just like the car.
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#8
as the game show said long ago
"Will the real P1875 please stand up!,." "what's my line"

and as we all know,FSM words are japan language translations, that are never ever all that good.
we also know the TCM brain is not the dreams of Alan Turing, the polar opposite of AI or any sort of expert machine.

The DTCs must be cured in the proper order and we all know false DTCs are common, and we know why, the above stated fact.
the Firmware is dumb, sure it shifts ok when all is good.
I am now betting the 1875 is just the one switch is bad.
It should say if the HI/low is bad, all vss errors are false. (we now know it runs 2 tables , for speed, 1 high, 1 low)
http://www.fixkick.com
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#9
(12-13-2019, 01:56 AM)fixkick Wrote: as the game show said long ago
"Will  the real P1875 please stand up!,." "what's my line"

and as we all know,FSM words are japan language translations, that are never ever all that good.
we also know the TCM brain is not the dreams of Alan Turing,  the polar opposite of AI or any sort of expert machine.

The DTCs must be cured in the proper order and we all know false DTCs are common, and we know why, the above stated fact.
the Firmware is dumb,  sure it shifts ok when all is good.
I am now betting the 1875 is just the one switch is bad.
It should say if the HI/low is bad,  all vss errors are false. (we now know it runs 2 tables , for speed, 1 high, 1 low)

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.
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