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Discussion Starter · #1 ·
Well, it happened this afternoon.. stranded by a TCS/ETS Failure.

Car starts, I put the car in D, lift the brake and off it trundles... but as soon as i push the accelerator on comes the TCS CTRL lamp and the engine dies.

The electronic throttle body is relatively new (fitted in the last 7000KMS) and whilst I'm not discounting it's failure.. what else should I be looking at?

How exactly does the TCS/ETS system work?
 

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The TCS uses the ABS sensors to monitor wheel rotation and checks for differences (as far as I am aware)... so a iffy ABS sensor could cause problems.. It might be worth disconnecting the battery and leaving it for a bit to see if its just the ECU sulking.

Steve
 

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Is it a hard fault or a soft fault?

Did it roccur after a switch off?

I've had the TCS light com on in the carly once, after 230 hard pressed miles at 70... I came off the M6 at stoke south, slowed to the light and bang.

Switched off and left for 30 secs, switched on and I've never have another problem in over a year and 20,000 miles.

The Aero went into limp home just after I bought it (and was under warrenty) 3-4 time in rapid succession. Was diagmosed as a bad spot on the throttle potentiometer. Changed 6.5 years ago and all been OK since.

The CSET has had no TCS problems.

Andrew
 

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Mark,

Very sorry to hear about your problems.

While my car was at Trents they fitted two new throttle bodies. They ended up rejecting the first one Saab supplied at they couldn't get it properly calibrated. It's possible that there may be a few faulty units in the Saab spares system.

I used to have a link to some scanned in documents which explained the TCS system in detail. Currently using Google to find them again.
 

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Mark, best thing is to have the fault codes pulled. If the problem was an ABS sensor, I would expect to see the ABS light too. If you can press the accelerator fast enough to pick up the cable before the engine dies, you ought to be able to drive it. The idle speed in limp-home mode is very low.

Originally posted by Mark_A:
[qb]How exactly does the TCS/ETS system work? [/qb][/b]
Here it is as it applies to auto transmission models.

SYSTEM DESCRIPTION

Traction Control System (TCS) is used to prevent wheel spin when the car is accelerating on a slippery surface.
The TCS system for automatic transmissions consists of two subsystems, the Electronic Throttle System (ETS) and Automatic Slip Reduction (ASR).
TCS utilizes many of the components in the ABS system. The major addition to the system is the Electronic Throttle System.
Automatic transmission TCS does not have the capability to apply the brakes during wheel spin conditions, however this system does control the operation of the transmission kickdown cable in addition to controlling the throttle butterfly.

SUBSYSTEM DESCRIPTION ELECTRONIC THROTTLE SYSTEM (ETS)

The main purpose of the ETS system is to electronically control the position of the throttle butterfly.
The throttle housing is equipped with an actuating motor for the throttle butterfly, a vacuum unit, a throttle potentiometer and a safety cutout switch. Connected to the accelerator pedal is a pedal sensor with associated solenoid valves and a non-return valve fitted on the bulkhead. For additional safety, a parallel system using a throttle cable is provided, which will take over in the limp-home mode.

Automatic Idling Control (AIC)

The ETS eliminates the need for separate components for Automatic Idling Control (AIC) and load related control over the entire working range of the engine.

Smooth Response To Heavy-Footed Use Of Accelerator

If the driver depresses or releases the accelerator abruptly, the throttle butterfly will be operated in two steps within a period of just a few milliseconds. This allows the car responding smoothly on both acceleration and deceleration.

Integral Cruise Control Function

The ETS system incorporates a cruise control function. Since operation of the cruise control system is based on acceleration control, maximum engine performance is available under all conditions, unlike some previous systems which reverted to basic boost when cruise control was operating.

Intelligent System

The ETS is an intelligent or adaptive system, which means that it adapts itself automatically to changes in air pressure, humidity and variations due to wear in components.
The ETS also incorporates an AIC function for the warm-up phase, governed by time and coolant temperature.
The system continuously processes data from the speedometer, direct ignition system, ABS system, LH system and temperature sensor. It also monitors the position of the throttle butterfly and accelerator.
On the basis of this input data, the ECU controls the actuating motor for the throttle butterfly.

AUTOMATIC SLIP REDUCTION (ASR)
Vehicles with automatic transmissions utilize only the throttle butterfly for traction control. With the addition of a kickdown cable control, the ASR system can be described separately even though ASR is an integral part of the Electronic Throttle System (ETS).
Automatic transmission vehicles with traction control utilize another control unit to assist in operation of the kickdown wire (KDW). This additional ECU is on top of the ETS ECU which is fitting since the ASR ECU and the ETS ECU are basically one control unit.[/b]
Some more detail. The throttle housing description should be especially interesting. A common fault is failure of the safety valve (on the bulkhead behind the inlet manifold). Basically, loss of vacuum is one of a number of things that could cause limp-home.

THROTTLE HOUSING

The throttle housing controls the amount of air supplied to the engine, but the position of the throttle butterfly is controlled by means of a pulse width modulated motor.
A throttle cable is connected in parallel, for use in emergency limp-home mode.

Normal Mode

When the engine is started, a vacuum is raised in the vacuum unit. This causes the diaphragm and lever assembly to move upwards, which tensions the spring. This action also causes the throttle cable attachment lever to turn, slackening the cable and allowing the throttle butterfly to be controlled over idling to full throttle range by the motor. The motor actuates the throttle spindle through a link rod attached at either end to levers on the motor and spindle.

Limp-Home Mode

If a fault should occur anywhere in the system, a safety valve on the bulkhead immediately exhausts the vacuum in the vacuum unit.
The diaphragm rod and lever assembly moves down, tensioning the spring, to bring full spring force to bear on the throttle spindle. Since the motor is not powerful enough to overcome the force of the spring to operate the throttle butterfly, the throttle can only be operated by the throttle cable.
The car is now in the limp-home mode, which is clearly evident by both the additionally force required to move the accelerator and the fact that the TCS CTRL light has come on.

AUTOMATIC IDLING CONTROL (AIC)

Because the mass of air that the AIC valve admitted through the throttle housing to compensate idling speed for A/C cut-in etc. varies depending on pressure and temperature, the compensation it provides also tends to vary to some extent with ambient conditions.
However, because the AIC function in the ETS is adaptive, continuous compensation related to pressure and temperature takes place, which means that the opening duration and throttle angle will always be exactly right to admit the precise mass of air required for correct idling speed compensation. This means that ETS compensates for cut-in of power consumers not just on idling but throughout the engine speed range (except at full throttle).

CRUISE CONTROL

Cruise control function is incorporated in the ETS and is controlled by the ratio between torque and engine speed at any given instant, in accordance with the map curve in the ECU.
The throttle is adjusted to maintain the selected speed at any given moment and under all driving conditions (engine load conditions).
The system operation is automatically terminated if either the brake or clutch pedal is depressed or the switch is moved to the Off position.[/b]
 

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A bit more that I missed ...

Automatic Slip Reduction (ASR)

ELECTRONIC CONTROL UNIT (ASR ECU)

The ASR ECU has two functions; deciding when traction control mode is needed and operating the kickdown wire motor.
The ASR ECU is an addition to the ETS ECU. Both ECUs can be found below the driver's seat fixed to a mounting bracket. Several wires from the ASR ECU are connected to the ETS ECU, since the two units share many of the same signals.


KICKDOWN WIRE SETTING MOTOR

The kickdown wire (KDW) motor that controls the kickdown cable is located on a separate bracket on the engine frame adjacent to the steering rack.
The main purpose of the motor is to replace the lever on the conventional throttle valve housing, since the ETS throttle valve has no lever. Position of the KDW is proportional at all times to the actual position of the accelerator. The KDW motor includes a potentiometer which informs the ASR ECU of KDW position at all times.

Limp-Home Mode - Kickdown Wire

If a fault occurs in the ASR system, or in the ETS system which is critical to the operation of Traction Control, the system will revert to the limp-home mode.
In the limp-home mode, the kickdown wire is set to a fixed position of approximately 40 percent of full travel. At the same time, engine torque is limited to a maximum of 85 percent of normal through control of the throttle valve opening position.
This torque limitation combined with the fixed position of the kickdown wire help prevent any transmission slippage.

PEDAL & THROTTLE POTENTIOMETERS

The ASR ECU constantly compares the signal at pin 1 (pedal potentiometer position) with the signal at pin 3 (throttle potentiometer position). If there is an abnormal deviation between the two signals, the system will revert to the limp-home position.

WHEEL SPEED SIGNALS

The ASR ECU receives wheel speed information from the Antilock Brake System Electronic Control Unit (ABS ECU). The ABS ECU receives and AC. voltage from each wheel speed sensor, and converts the AC. voltage to a digital square wave. As the speed of the wheel increases, the frequency of the AC. voltage increases, so the ABS ECU increases the frequency of the digital square wave. Test pulses are generated by the ABS ECU so that the ASR ECU can check for continuity of the signal wires even when the car is stationary.
If there is a deviation in the speed of either front wheel when compared with the reference speed (average rear wheel speed), the ASR ECU sends a signal to the ETS ECU to decrease the throttle opening to stop the wheel spin.

GEAR SELECTOR SIGNAL

The ASR ECU receives information from the gear selector switch regarding gear selector position. When the gear selector is in Park or Neutral there is no signal (zero volts). When the gear selector is placed in any driving position, the ASR ECU receives a 12 volt signal. The ASR ECU then sends a signal to the ETS ECU for idle compensation.[/b]
 

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Discussion Starter · #8 ·
Thanks everyone..

Well, the ABS lights took quite a bit of time to switch off usually after engine fire up, but never come on during driving.

The TCS CTRL lamp flickered on a little sometimes (but never full brightness).. but it never affected the driving of the car, until now.

TCS had been working fine up-till-now in the snowy bad weather this week.
 

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Sorry to butt in chaps. But I had the clip that holds the throttle cable onto the throttle body break off just before christmas but fortunately I had a replacement to hand. But ever since because it made the TCS light illuminate it has had check engine permanently on. I know that I need the ECU resetting but didn't someone once mention on here that if you disconnect the ECU from the battery it will automatically reset itself after a certain amount of time, inlcuing any error codes/lights.
 

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Discussion Starter · #10 ·
My ECU showed the following errorcodes when my guy pulled them with Tech2..

Any ideas what they mean?

25721
25771
33450
D75B2

The car has suddenly started working fine again.. and is showing no hint of TCS failure.. it drives great and when I plant the throttle, the yellow TCS lamp comes on (as it should) as the car controls wheel spin..
 

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25721 - Pedal switch constantly off (intermittent fault)
25771 - Pedal switch constantly on (intermittent fault)
33450 - Safety valve current low (intermittent fault)
D75B2 - Communication error, communication interrupted (intermittent fault)

Certainly sounds as though you have a problem with the pedal switch, wherever that is.
 

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Originally posted by BillJ:
[qb]25721 - Pedal switch constantly off (intermittent fault)
25771 - Pedal switch constantly on (intermittent fault)
33450 - Safety valve current low (intermittent fault)
D75B2 - Communication error, communication interrupted (intermittent fault)

Certainly sounds as though you have a problem with the pedal switch, wherever that is. [/qb][/b]
That'll be in the throttle body, as the accelerator is cable until up to the point where it's "clamped" into the ETS mechanism. May be a cheap repair providing you don't have to crack open the throttle body to get at it.
 

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Discussion Starter · #14 ·
Thanks guys, car seems perfectly fine right now..

From Bill's explaination..

Connected to the accelerator pedal is a pedal sensor with associated solenoid valves and a non-return valve fitted on the bulkhead. For additional safety, a parallel system using a throttle cable is provided, which will take over in the limp-home mode.[/b]
So it could well be outside the throttlebody.
 
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