Oxygen Sensor Woes... Technicians please help, diag info included. (1 Viewer)

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Aug 29, 2018
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CO
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I've got a 96 FZJ80, 1FZ. Check engine light on with a p0171 system too lean code. Engine runs great but the long term fuel trim is at like +20%. NO voltage from the front oxygen sensor, vehicle is stuck in open loop.

I have battery voltage on the yellow/red wire to the sensor, ground at the grey heater wire and good ground on the brown/black wire.
No voltage from the blue wire on the sensor, FWIW the heater monitor did pass on the scan tool so I know for sure the heater is good, it ohms out as well.

On the ECU pins I have continuity on the blue signal wire from the ECU to the sensor, same goes for the gray heater wire, power and grounds are good. So That made me think the ECU may be bad, shorted internally. Swapped in another ECU and still nothing.


I'm completely stumped, the vehicle has a brand new NTK oxygen sensor (front) so I HIGHLY doubt the sensor is bad, wiring seems to check out, so what else am I missing?

Only other thing i can think to try is running a jumper wire in place of the blue wire to rule out being shorted or open somewhere.

:bang::bang::bang:
 
Last edited:
Joined
Nov 9, 2012
Messages
10,663
Location
Olathe, KS, USA
I've got a 96 FZJ80, 1FZ. Check engine light on with a p0171 system too lean code. Engine runs great but the long term fuel trim is at like +20%. NO voltage from the front oxygen sensor, vehicle is stuck in open loop.

I have battery voltage on the yellow/red wire to the sensor, ground at the grey heater wire and good ground on the brown/black wire.
No voltage from the blue wire on the sensor, FWIW the heater monitor did pass on the scan tool so I know for sure the heater is good, it ohms out as well.

On the ECU pins I have continuity on the blue signal wire from the ECU to the sensor, same goes for the gray heater wire, power and grounds are good. So That made me think the ECU may be bad, shorted internally. Swapped in another ECU and still nothing.

I'm completely stumped, the vehicle has a brand new NTK oxygen sensor (front) so I HIGHLY doubt the sensor is bad, wiring checks out, so what else am I missing?

:bang::bang::bang:
Not hitting closed loop due to temp sensor not giving proper info to ECU?
 

ppc

M Go Blue
Joined
Aug 18, 2003
Messages
3,366
Location
Nashville, TN
Why was the O2 sensor replaced?
Did the PO171 or other code exist previously?
In a 96 model the OEM O2 sensor would have been a Denso brand.
The 93-94 models are the ones that use a NTK brand as OEM.
It might be time to replace the O2 based upon that alone. Keep in mind that just because a part is relatively new doesn't mean it hasn't failed.
 
Last edited:
Joined
Jul 16, 2013
Messages
401
Location
East Hampton, CT
Any updates? My po141 o2 sensor code came back on. Im not getting voltage at bank 2 pin on ecm. Contemplating replacing ecm or maybe temp sensor. Wondering if maybe you solved your issue?
 

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