P0134 p0154

99 gm suburban 5.7.all 4 02 sensors share power and ground. All 4 02 sensors were replaced aftermarket 02s.can aftermarket 02s be a problem on an older gm?

P0134, p0154: no activity detected on 02s b1s1/b2s1 (respectively).

I would start with a quick check of the heater circuits. No heater=delayed response.
Then a check of scan data while manipulating the mixture by adding propane to the intake and creating a vacuum leak to see if there sensors respond accordingly.

Thanks for the reply. Going check that out just thought strange that flagged both upstream 02 sensors all 4 share same power and ground.

Test light between power and ground for both precat 02 sensors heater circuit koeo test light lights. Koeo test light connected to battery negative and touch 02 signal wires on both precat 02 sensors scan data stays at 450 mv. Going to check what bias voltage getting on the signal wires at 02 sensors. Possible open in the harness? Any ideas?

your test show the wiring integrity is good, the problem is the 02's. With GM's the bias voltage is 450mv.

Sorry, I was wrong here... I should have read the post more closely...

The customer replaced all 4 02 sensors.

autojoe wrote: Test light between power and ground for both precat 02 sensors heater circuit koeo test light lights. Koeo test light connected to battery negative and touch 02 signal wires on both precat 02 sensors scan data stays at 450 mv.

Bias voltage should drop.

Going to check what bias voltage getting on the signal wires at 02 sensors. Possible open in the harness? Any ideas?

You're on the right track.

scannerjohn wrote: your test show the wiring integrity is good, the problem is the 02's. With GM's the bias voltage is 450mv.

This testing suggests that the bias voltage is NOT reaching the connector. If it was, the test light would pull the 450mV to ground. Cranking the engine may update scan data.