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 DIAGNOSISENGINE PERFORMANCETESTING & DIAGNOSISON-BOARD DIAGNOSTIC [ENGINE CONTROL SYSTEM (AJ]DTC P0138, P0158 [AJ]NOTES

2008 Mazda 6 s Sport, 4D Hatchback, Standard

DTC P0138, P0158 [AJ]: Notes

2008 Mazda 6 s Sport, 4D Hatchback, StandardSECTION Notes

DTC P0138, P0158 [AJ] DETECTION CONDITION AND POSSIBLE CAUSES

DTC P0138
DTC P0158

HO2S (RR) circuit high input
HO2S (LR) circuit high input

DETECTION CONDITION

The PCM monitors input voltage from front HO2S (RR, LR). If the PCM detected HO2S (RR, LR) voltage above 1.2 V for 0.8 s , the PCM determines that the circuit input is high.

Diagnostic support note

This is a continuous monitor (HO2S).
MIL illuminates if the PCM detects the above malfunction condition in two consecutive drive cycles or in one drive cycle while the DTC for the same malfunction has been stored in the PCM.
PENDING CODE is available if the PCM detects the above malfunction condition during the first drive cycle.
FREEZE FRAME DATA is available.
DTC is stored in the PCM memory.

POSSIBLE CAUSE

HO2S (RR, LR) malfunction
Short to power supply in the wiring harness between the following terminals:
- For P0138: HO2S (RR) terminal A and PCM terminal 2AG
- For P0158: HO2S (LR) terminal A and PCM terminal 2AH
HO2S (RR, LR) or PCM terminal is shorted
PCM malfunction

RENDER: 1.0x

NO RELATED

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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.