Step 1 - Locate the diagnostic box which is usually under the hood near the left strut, this box is about two inches by four inches.
Step 2 - Remove the protective cover and locate a button next to a red led light, which is used to blink out a trouble code which will be identified by flashing on and off.
Step 3 - Start the code gathering procedure by turning the ignition key to the "ON" position without starting the engine, push the button down for three seconds. The light will flash a number of times, followed by a three second pause dividing the trouble code digits.
Step 4 - For example; the light blinks once, then pauses, blinks two more times, and pauses and then finishes with five more blinks, the trouble codes will be 125.
Step 5 - After repairs have been made, clear the codes by turning the key to the "ON" position without starting the engine, push the button down for five seconds and release, after three seconds the light will illuminate, press the button for five more seconds and release, the codes should be cleared, the codes can also be cleared by disconnecting the battery.
Volvo Diagnostic Code Definitions
111 No faults.
113 Fuel injectors.
113 Heated Oxygen sensor max enrichment sensed
115 Injector #1.
121 Mass airflow sensor.
122 Air temp sensor signal.
123 Coolant temp sensor signal.
125 Injector #2.
131 Ignition system RPM signal.
132 Battery voltage.
133 Throttle switch signal (idle).
135 Injector #3.
142 ECU faulty.
143 Knock Sensor signal missing or defective.
144 Fuel system load signal (missing or defective).
145 Injector #4.
153 Rear heated oxygen sensor signal.
154 EGR system leakage or excessive flow.
155 Injector #5.
212 Oxygen sensor signal (front sensor on 94 and later models).
213 Throttle switch signal.
214 Ignition RPM signal erratic.
221 Heated Oxygen Sensor (Rich mixture/part throttle).
222 Main relay.
223 Idle valve signal.
224 Coolant temp sensor signal.
225 A/C pressure sensor signal.
231 Lamba adjustment.
231 Heated Oxygen sensor (lean mixture/part throttle) 94up.
232 Lamda adjustment.
232 Adaptive heated O2 sensor control (94up).
233 Idle valve closing signal.
234 Throttle switch signal missing.
241 EGR malfunction.
245 Idle air control valve closing signal.
311 Speedometer signal.
314 Camshaft position signal missing or defective.
315 EVAP emission control system.
321 Cold start valve signal missing.
322 Airflow meter hot wire.
324 Camshaft position signal erratic.
325 ECU memory failure.
335 TCM request for MIL.
411 Throttle switch signal faulty or missing.
413 EGR temp sensor signal incorrect or missing.
414 Turbo boost regulation.
416 Turbo boost reduction from TCM.
425 Temp warning level #1.
431 EGR temp sensor faulty or missing.
432 High temp warning inside ECU.
433 No rear knock sensor signal.
435 Front heated oxygen sensor slow response.
436 Rear heated oxygen sensor compensation.
443 Catalytic converter efficiency.
444 Acceleration sensor signal.
451 Misfire #1 cylinder.
452 Misfire #2 cylinder.
453 Misfire #3 cylinder.
454 Misfire #4 cylinder.
455 Misfire #5 cylinder.
511 Adaptive oxygen sensor control lean mixture at idle.
512 Oxygen integrator at max lean running limit.
513 High temp warning inside ECU.
514 Engine cooling fan low speed signal faulty.
521 Oxygen sensor preheating front.
522 Oxygen sensor preheating rear.
531 Power stage group A.
532 Power stage group B.
533 Power stage group C.
534 Power stage group C.
535 TC control valve signal.
541 EVAP valve signal.
542 Misfire more than one cylinder.
543 Misfire at least one cylinder.
544 Misfire more than one cylinder/catalytic converter damage.
545 Misfire at least one cylinder/catalytic converter damage.
551 Misfire #1 cylinder/catalytic converter damage.
552 Misfire #2 cylinder/catalytic converter damage.
553 Misfire #3 cylinder/catalytic converter damage.
554 Misfire #4 cylinder/catalytic converter damage.
555 Misfire #5 cylinder/catalytic converter damage.