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Discussion Starter · #1 ·
I was hoping that someone could shed some light on the source of a 4C problem I am having.

Setup: Eibach Pro springs, IPD track spec f&r, 30mm spacers f&r, PS2 summers on 18s, ride height LR/RR ~13.5".

I received the "chassis settings service required" code on the dash, suspension went to limp (felt less dampened than 4C disabled?) mode, intermittent indications on the 4C leds. Brought the car in, DTC permanent errors for the rear position sensors and the SUM. Replaced sensors and SUM, couldn't cal, raised RR buy hand and cal'd ok. Suspension at this point: 4C buttons now work, suspension still in limp.

Back on the Volvo CPU today, checked SUM ver - current, SUM reloaded for S&G anyway, raised rear to stock ride height and ran the cal. We checked the electrical loading to each of the shocks and they were cycling as expected. The right rear pos sensor is 1.5V and the left is 3.5V (is this delta normal?).
At this point the suspension problem was corrected and no codes.

On the way home from work, "chassis settings....." Based on the above description I am not sure if the source of my problem is spring related or there is another potential culprit. I plan on getting the car back in to see what the codes are and if they are the same, should I have them replace the springs with TMEs to get a closer to stock ride height? and have them replace the sensors/potentially SUM (assuming fault codes) while they are at it?

The dealership was excellent throughout the process as they installed the springs, but I don't want to develop a negative relationship. I don't know how much sensors/SUM cost to replace so I don't know how many repeat events it will take before they start pointing to the springs (see "R" Kelly).

Any help on this would be greatly appreciated.
 

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Re: Tech assist on 4C failure (martynunya)

Quote, originally posted by martynunya »
I was hoping that someone could shed some light on the source of a 4C problem I am having.

Setup: Eibach Pro springs, IPD track spec f&r, 30mm spacers f&r, PS2 summers on 18s, ride height LR/RR ~13.5".

The right rear pos sensor is 1.5V and the left is 3.5V (is this delta normal?).

No I would not expect that type of delta unless one side of the car is significantly higher than the other. Nominal is 2.5 volts. I do not know what type of range the SUM calibration routine has and whether it can or can not accept these values as normal, static values. Clearly they are acceptable values in a dynamic situation.
 

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As far as I recall, in terms of position sensor values, one side is supposed to read high while the other is supposed to read low. What you had seems about right. Lowering springs do put the sensors near the allowable limits. My dealer had to jack up the rear end a little just to get the 4C to calibrate, after that no issues for me - i.e., the 4C did not go into a "limp mode".
 

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Discussion Starter · #4 ·
Could a failed shock cause the low reading on the RR sensor and not throw a shock code? The shocks did check out electrically, is there a more difinitive test for the shocks?
 

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There are two position sensors at the rear suspension. The position sensor measure the position of the right and left-hand control arms in relation to the car body. The vertical position of the shock absorber is calculated based on this position. The sensors are supplied with 5 V by the suspension module (SUM). When the vehicle is stationary, the output signal from the sensors is approximately 2-3 V. When there is vertical movement the signal will oscillate around these values (min 0.5V, max 4.5V); the greater the movement the greater the deviation.
Note! The values move in different directions on the left and right-hand sides. Upwards body movement results in increased voltage on the left-hand side and a voltage drop on the right-hand side.

The shocks have their own separate VADIS test values...don't have them on hand.
 

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Re: (martynunya)

Quote, originally posted by martynunya »
Could a failed shock cause the low reading on the RR sensor and not throw a shock code? The shocks did check out electrically, is there a more difinitive test for the shocks?

No. The shock is independent of the sensor. The shock has no "sensor" function in it. It is a simple electromagnetic valve, a solenoid whose plunger controls the size of the valve orifice. Clearly if there is a hydraulic failure in the shock, the shock is worthless however it has no way of reporting that back to the SUM.

It is more important that the position sensors have a full range, and BLOT has suggested these values, I would detach the sensor linkage and be sure that they have the range of values given.

In terms of looking at the electrical side of the shock, I would just confirm that there is an appropriate DC resistance from the SUM to the shock. My car is not here right now for me to measure these values, but I would expect something on the order of 10 Ohms. Clearly it should not be 0 nor should it be infinite. Remember this only tests the electrical winding of the solenoid, not necessarily that the internal valve is functioning properly, but again all the SUM cares about is seeing the appropriate "load".
 

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Discussion Starter · #7 ·
Sorry, a better question should be: if a shock has failed mechanically, could this cause a difference in ride height and therefore force the pos sensor to report an out of range value?
I am just trying to find out if another 4C component could be causing the failures of the pos sensors and the sum. If not, then I guess I should buy some new springs and see if this fixes the problem.
 

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Re: (martynunya)

I seriously doubt that new springs are in order. Why? I've had my eibachs on for quite some time, and have never had any 4C codes be thrown (I also didn't have to jack up the rear of my car to calibrate the SUM).

My first point to start the diagnosis would be to re-examine the 4C components that were affected during the spring instal. Specifically, the ride height position sensors. Volvo does a pretty good job of minimizing "wiggle room" with the sensor mounting points, but there still remains the possibility that the sensor mounts weren't re-installed exactly where they should be.

I would loosen the sensor mounting points, and using any play room available, I would try to lower the mounting point as much as possible (thereby causing the 4C to think the rear is higher than it really is). Do that, calibrate the SUM, and then see if you get any codes.

A mechanical shock failure shouldn't throw a 4C code. I would still check for a mechanical failure though. Tell-tale sign would be fluid leaking from the shock (for what it's worth, we've replaced several shocks on R cars that had stock springs in them, and we've seen no increase is shock failure on cars with non-stock springs vs. stock). The other thing I would recommend would be to function test each shock, in each chassis setting. With the car running and in comfort, check the compression and rebound at all for corners . . . then re-check in each chassis setting. If one shock is bad, you'll be able to notice a difference.

Lastly, check your tire pressures. If you feel a change when you press the chassis buttons (i.e. you can feel the difference between comfort and advanced), but it still feels "soft," it could be that your pressures are low -- that wouldn't cause a DTC, but it would affect the feel.
 

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Discussion Starter · #9 ·
Re: (R Salesman)

The springs and sways have been installed since March, haven't had any issues until now.
We examined the rear shocks for leaking fluid and didn't find any. All of the tire pressures were ~38 psi. No change in feel when shifting 4C to comfort, adv, sport. I did notice a slight difference when 4C was disabled.

I think that I may have the same failure codes now on the new sensors and sum as I did on the ones that were replaced this week. Regarding the shock function test, should I look at the pos sensor voltage when bouncing around all four corners or is there another screen that displays shock loading?
 

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Re: (martynunya)

Quote, originally posted by martynunya »
Regarding the shock function test, should I look at the pos sensor voltage when bouncing around all four corners or is there another screen that displays shock loading?

Just do it by feel. R/F, L/F should feel the same, etc.

If you've already replaced the sensors AND the SUM, then the culprit obviously lies elsewhere. The mechanical functionality of the shocks won't set a code, so for fault-tracing purposes they don't matter.

My guess is that the control unit (i.e. the switches in the dash) needs to be replaced.
 

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Discussion Starter · #11 ·
Well, fwiw the two rears feel the same as does the front. I forgot I couldn't change the 4C mode in limp.
Do you think that the dash switch could have caused a failure in the SUM? The lights have been intermittently changing, sometimes displaying both comfort and sport, comfort and advanced etc. When the 4C is disabled, no matter what I had previously with the switch, it forces it back to sport and clears dual indications.
 

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Re: (martynunya)

I read that the multiple lights on the chassis settings was directly related to the control unit on the dash failing. Once that was replaced all was fine.(I can't find that post but it was up about 3 weeks ago)Should be an easy fix. Rick
 

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Discussion Starter · #14 ·
Well here goes, the techs played around with the fit on the rear pos sensors, the car now cals fine at the Eibach ride height with no softness in the suspension. The 4C controller was replaced and the car ran fine for the better part of a day and then displayed abnormal settings (adv and sport). Tomorrow the Volvo rep is coming to take a look at it.

The only things left are the springs, shocks and the accelelorometers in the front. Is it possible that there is another electronic unit causing this problem (ECU)? The tech mentioned this, but I am not smart enough on ECU/4C interface to know if this situation is even possible.
 

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Re: (martynunya)

ECU and the SUM are separate, one has nothing to do with the other.
Now the CEM (the central module) oversees everything. SOmetimes the CEM needs a reload.
(ALL settings will then go back to default and sometimes have to be reentered)
 
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