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 MANUALSMAZDA20086 S SPORT, 4D HATCHBACK, STANDARDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 46 (ENGINE CONTROLS - SELF-DIAGNOSTICS)SYSTEM TESTSPCM POWER RELAY
2008 Mazda 6 s Sport, 4D Hatchback, Standard
Pcm Power Relay
2008 Mazda 6 s Sport, 4D Hatchback, StandardSECTION Pcm Power Relay
WARNING: This page is about a different car, the 2002 Mazda B4000, 2002 Mazda B3000, and 2002 Mazda B2300. However, it is still accessible from the selected car via links, so may be relevant.
- Check VPWR Circuit Resistance
Disconnect Idle Air Control (IAC) valve electrical connector. Disconnect scan tool from DLC. Disconnect PCM power relay. Measure resistance of VPWR circuit (Red wire) between IAC valve harness connector and PCM power relay connector. If resistance is less than 5 ohms, reconnect IAC valve. Go to next step. If resistance is 5 ohms or more, repair open VPWR circuit between PCM power relay and splice to IAC valve. See WIRING DIAGRAMS article. Restore vehicle. Rerun QUICK TEST under SELF-DIAGNOSTIC SYSTEM. - Check B+ & IGN START/RUN Voltage To PCM Power Relay
Measure B+ circuit (Yellow wire) at PCM power relay connector. Record reading. With KOEO, measure voltage of IGN START/RUN circuit (Tan/Black wire) at PCM power relay connector. Record reading. If both voltage readings are more than 10.5 volts, go to next step. If either voltage reading is 10.5 volts or less, turn ignition off. Repair open in B+ circuit (Yellow wire) or IGN START/RUN circuit (Tan/Black wire), and verify condition PCM diode. See WIRING DIAGRAMS article. Restore vehicle. Rerun QUICK TEST under SELF-DIAGNOSTIC SYSTEM. - Check Ground Circuit To Power Relay
Measure voltage between B+ circuit (Yellow wire) and ground circuit (Black/White wire) at PCM power relay connector. Turn ignition off. If voltage is more than 10.5 volts, replace faulty PCM power relay. Restore vehicle. Rerun QUICK TEST under SELF-DIAGNOSTIC SYSTEM. If voltage is 10.5 volts or less, repair open ground circuit. See WIRING DIAGRAMS article. Restore vehicle. Rerun QUICK TEST under SELF-DIAGNOSTIC SYSTEM.
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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.