Random Question - CEL 25/26 (1 Viewer)

[sierra1boy]

Guys, random question I’ve been chasing down these two codes for a while by troubleshooting and repairing the emission system. However, around the same time I noticed that my radiator was very low. Once I filled it up the codes went away. Is there a chance that the cooling system could have been driving those two codes?

 

[Malleus]

Here's the system diagram:

There's no coolant interaction with the SFI system, so I don't see how.

But I've been wrong before.

 

[Malleus]

There are two engine coolant temperature sensors in the head; one for the combination meter gauge and one for the ECM. The ECM sensor is the ECT sensor:

Nothing jumps out at me that would indicate a relationship between engine coolant temperature, would have been erroneous if the coolant was low, and the exhaust temperature or air/fuel ratio.

 

[Malleus]

The only coolant near the SFI system is the water bypass circuit that is intended to warm the air in the throttle body, to aid cold engine operation. But that's not "in" the EGR or A/F sensor circuits, however, the 3rd generation 80 series has a DTC P0125, Insufficient Coolant Temp for Closed Loop Fuel Control, which is referenced in the related P0130 DTC, Heated Oxygen Sensor Circuit Malfunction. It's unclear from the manual exactly how this is related to the P0130 DTC, however, unless it's only in the manual so that the technicians know to test only after the engine is warm, which wouldn't be obvious if the sensor was faulty.

That's purely a guess on my part.

From the 1995 service manual:

I mention this purely for the sake of completeness, I've never tried to compare the "programming" between 2nd and 3rd generation 80 series.

 

[jonheld]

Guys, random question I’ve been chasing down these two codes for a while by troubleshooting and repairing the emission system. However, around the same time I noticed that my radiator was very low. Once I filled it up the codes went away. Is there a chance that the cooling system could have been driving those two codes?

OBD1 codes 25/26 are almost always related to O2 sensors on a 3FE and 1FZ engine.

 

[bigredmachine]

i was chasing down thse codes as well and found that the rear o2 sensor harness had rubbed through on the front drive shaft and poor wire repairs was causing the codes.

start with the basics, fix any exhaust leaks in front of the o2 sensors, check the wire harness and o2 sensor plugs for corrosion, test the o2 sensors as per the fsm then go from there

 

[sierra1boy]

Some greatbinformatio guys, thank you.

I just remembered that around the same time that I had the radiator fluid issue I had changed out the vacuum modulator. Maybe that was it??