Possible Causes
WARNING: This page is about a different car, the 2003 Mazda 6. However, it is still accessible from the selected car via links, so may be relevant.
Possible causes are:
- Right or left rear HO2S malfunction
- PCM malfunction
- Short to power circuit between right or left rear HO2S terminal and PCM terminal:
- For P0138: Right rear HO2S 4-pin harness connector terminal "A" and PCM 104-pin harness connector terminal No. 35 (White wire)
- For P0158: Left rear HO2S 4-pin harness connector terminal "A" and PCM 104-pin harness connector terminal No. 61 (Red wire)