Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSVOLVO2001S40 L4-1.9L TURBO VIN 29 B4204T3REPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTCOMPUTERS AND CONTROL SYSTEMSDESCRIPTION AND OPERATIONSYSTEM OVERVIEW
2001 Volvo S40 L4-1.9L Turbo VIN 29 B4204T3
System Overview
2001 Volvo S40 L4-1.9L Turbo VIN 29 B4204T3SECTION System Overview
Overview
General
The DSA control module has an integrated diagnostic system, the Volvo on-board diagnostic (OBD) system. This system continuously monitors itself and the input and output signals.
Diagnostic trouble codes (DTCs)
A diagnostic trouble code (DTC) is stored and the DSA warning lamp lights if the control module detects a fault. The exception is diagnostic trouble code (DTC) DSA-122 DSA warning lamp. This DSA warning lamp cannot be activated if this fault is stored.
Faults, with the exception of diagnostic trouble code (DTC) DSA-122 DSA warning lamp, disengage the DSA function. If diagnostic trouble code (DTC) DSA-122 DSA warning lamp is stored, the warning lamp cannot be used to determine whether the DSA function is engaged or not. The DSA function is then always engaged and cannot be disengaged manually.
If the DSA warning lamp is lit, the DSA function is not operating normally or it is not engaged.
If a fault disappears for any reason (becomes intermittent) after the diagnostic trouble code (DTC) has been permanently stored in the control module, information about the fault remains in the control module.
Other
Every diagnostic trouble code (DTC) has a counter. The counter records the number of fault-free cycles since the diagnostic trouble code (DTC) was stored (intermittent fault). A cycle is defined as the first time the engine speed exceeds 600 rpm in the same interval in which the ignition is switched on (the engine starts) and then switched off. If diagnostic trouble code (DTC) DSA-221 Load signal is stored permanently, the cycle is defined as the first time the average wheel speed exceeds 50 km/h in the same interval in which the ignition is switched on (the engine starts) and then switched off. When a counter is at 0, the control module interprets the fault as permanent. If the counter value is greater than 0, the control module interprets it as no fault (intermittent fault). If the fault recurs, the counter is reset to zero. When the counter reaches 254 (i e. 254 fault-free cycles), the counter is no longer updated.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.