Diagnostic trouble codes (DTCs)
When a fault occurs it is stored in the control module as a diagnostic trouble code (DTC) provided that road speed has been above 35 km/h for at least 15 seconds.
Diagnostic trouble codes (DTCs) can be stored in the control module memory only as long as the ignition is on. When the ignition is switched off these diagnostic trouble codes (DTCs) are erased. The control module will detect diagnostic trouble codes (DTCs) again when vehicle speed has been above 35 km/h for at least 15 seconds.
Reading and erasing diagnostic trouble codes (DTCs)
Used for reading off and erasing diagnostic trouble code (DTC)s stored in the control module.
The on-board diagnostic (OBD) system can identify four types of fault in the form of diagnostic trouble codes (DTCs).
For a list of diagnostic trouble codes (DTCs) and fault-tracing, see Response and Diagnostic Trouble Code (DTC) tables .
HINT
HINT: The cruise control on-board diagnostic (OBD) system differs from most other systems' diagnostic functions in that diagnostic trouble codes (DTCs) are only stored in the control module until the engine is turned off. So it is important not to switch off the ignition after a test drive until any diagnostic trouble codes (DTCs) that have been stored have been read off.
HINT: Another difference is that the control module must receive a vehicle speed signal (VSS) above 35 km/h for at least 15 seconds before it will store diagnostic trouble codes (DTCs).
Note. Diagnostic trouble code (DTC) 1-1-2 will always be stored if the engine is turned off after a test drive. The test drive must then be carried out again.
Erasing diagnostic trouble codes (DTCs)
- by turning the engine off
- using the Volvo Scan Tool (ST) when the diagnostic trouble code (DTC) has been read off at least once.
Response and Diagnostic Trouble Code (DTC) tables
Note. Switch off ignition when connecting and disconnecting connector. Otherwise the control module could be damaged.
| Response code | Response text |
|---|---|
| 1-1-3 | Checking ON/OFF selector switch, brake and clutch valves |
| 1-2-3 | Checking RESUME switch |
| 1-3-1 | Checking SET+ switch |
| 2-1-3 | Checking SET- switch |
| 1-3-2 | Checking the brake light switch |
| 2-2-3 | Checking Park/Neutral Position switch (PNP) (automatic transmission) |
| 3-1-1 | Multiple simultaneous signals |
Confirmation of component activation (MODE 2)
| DTC | Fault message |
|---|---|
| 1-1-2 | Illegal vehicle speed signal |
| 1-2-2 | Vehicle speed has not exceeded 35 km/h (22 mph) or no vehicle speed signal |
| 2-1-1 | Internal fault in control module |
| 2-1-2 | Fault in vacuum pump or regulator circuit |
Diagnostic Trouble Codes (DTCs)
| Response code | Response text |
|---|---|
| 1-1-4 | Safety disengagement |
| 1-4-1 | Startinhibitor |
| 4-1-1 | Switch, brake or clutch |
| 1-2-4 | Brake light |
| 2-1-4 | Supply / not connected |
Read input and output signals (MODE 5)
Scheme 344
Control module
The control module compares selected speed with actual speed. If necessary the control module activates a vacuum pump or regulator, which in turn control a vacuum servo. This servo is connected to the accelerator pedal (AP) and therefore controls vehicle speed.
The selected speed is stored in the control module memory until the cruise control is disengaged by moving the switch on the direction indicator stalk to the OFF position, or until the speed stored in memory is changed by using SET+ or SET-.
The control module incorporates several safety functions to prevent damage due to system failures. Vehicle speed must be above
35 km/h (22 mph); the selector switch must be in the ON position, and the SET button must be pressed in before the control module can operate the vacuum pump relay. If the car has automatic transmission the control module is switched off when the gear selector lever is in the P or N positions.
In addition to electrical safety functions there are several pneumatic safety devices, see Vacuum control.
The control module monitors the system and disengages cruise control during abnormal acceleration (wheel-spin) or deceleration (wheels locking). The control module also disengages the system if vehicle speed drops below 75% of the selected speed. This may occur when driving up steep slopes when the engine cannot maintain a constant speed.
Another important control module function is to store diagnostic trouble codes (DTCs) allowing fault-tracing using the Volvo Scan Tool (ST).
In order to operate correctly the control module requires several sensors. These are described below with their functions.
Scheme 345
Stop (brake) light switch
The stop (brake) light switch acts as an extra safety device in case the brake pedal is depressed and the vacuum valve does not open. When the brakes are used the control module is no longer grounded via the stop (brake) light bulbs and the system is disengaged. If the bulbs are defective cruise control will not operate. Always check the stop (brake) light bulbs first if there is a fault in the system.
Scheme 346
From 1995- there is a new type of stop (brake) light switch, however, its function is the same.
Scheme 347
Pedal valves (electrical)
These are located above the brake pedal and clutch pedal (manual transmission) and have the same function as the stop (brake) light switch. They cut off the supply to the pump and regulator in the pump unit. This opens the pump regulator and allows air into the vacuum system. Normally when the pedal is up the valve is closed.
The pedal valves are combined electrical/vacuum valves. When the pedal is depressed the vacuum circuit is broken.
Scheme 348
Selector switch
The switch incorporates
- a switch for switching the system off and on
- two buttons to increase and decrease vehicle speed.
- a sliding switch to resume the selected speed.
Scheme 349
Vacuum pump and regulator
If vehicle speed drops the vacuum pump is turned on and the vacuum in the servo increases. The servo presses down the accelerator pedal (AP) a little and vehicle speed increases again. If vehicle speed increases the regulator allows air into the vacuum system reducing the vacuum. The vacuum pump is driven by an electric motor. This is switched on when the SET+ button is pressed in and the control module relay is operated. The motor drives the pump until the vacuum servo has a sufficient vacuum to maintain the selected speed.
When extra power is required, when driving up a hill for example, the vacuum pump is switched on again in order to increase the system vacuum until the selected speed is achieved. When driving downhill the regulator vacuum valve is opened to allow air into the system, reducing the vacuum to the vacuum servo.
Scheme 350
Park/Neutral Position Switch (PNP)
The control module is switched off when the automatic transmission gear selector lever is in the P or N positions. However, the selected speed is stored in memory.
Scheme 351
Vehicle speed signal (VSS)
The cruise control module requires information about the actual vehicle speed. This information is obtained from the speedometer. In cars with manual transmission the mechanical movement of the speedometer cable is converted into a speed-related pulsed frequency via a reed element switch in the instrument panel. This signal is then transmitted to the control module. In cars with automatic transmission this information is provided by the Aisin Warner transmission. This cable is routed to the instrument panel.
Data from all these sensors allow the control module to control vehicle speed. Actual speed control is carried out using a vacuum servo next to the accelerator pedal (AP). The vacuum for this servo is governed by a pump or control valve, the regulator.