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.

SYS.OK|MANUAL.DB● LIVE

HOMESERVICE MANUALSMAZDA20105 SPORT, 2.3 L, STANDARDREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMON-BOARD DIAGNOSTIC [ENGINE CONTROL SYSTEM L3]DTC P0138NOTES

2010 Mazda 5 Sport, 2.3 L, Standard

DTC P0138: Notes

2010 Mazda 5 Sport, 2.3 L, StandardSECTION Notes

DTC P0138 [L3] DETECTION CONDITIONS AND POSSIBLE CAUSES

DTC P0138

HO2S circuit high input

DETECTION CONDITION

The PCM monitors input voltage from HO2S. If the input voltage from the HO2S is above 1.2 V or HO2S bias voltage above 1.7 V for 5 s , the PCM determines that circuit input is high.

Diagnostic support note

This is a continuous monitor (A/F sensor, 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 (Mode 2/Mode 12) is available.
DTC is stored in the PCM memory.

POSSIBLE CAUSE

HO2S or PCM terminal is shorted
Short to power supply in the wiring harness between HO2S terminal A and PCM terminal 2Q
HO2S malfunction
PCM malfunction

Courtesy of MAZDA MOTORS CORP.

RENDER: 1.0x

NO RELATED

Recommended Tools & Savings

Use the Manual With the Right Hardware

Pair factory procedures with proven DIY tools so the instructions are easier to execute.

Affiliate disclosure: We may earn a commission at no extra cost to you.

Shop Manual-Ready Tools Free Quote Check Quote Shield Pro

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.