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Did I find Two problems withthe PCM?
2 months 1 day ago - 2 months 1 day ago #64784
by A.Bernier
This maybe confusing , I'll try to keep it clear.
2005 Toyota Tacoma 4.0 Vin U 4WD.
Was dropped at other garage, not running. They performed tune up and B1S1 due to a P0051 Heater circuit fault.
They did get the truck running, (not well) Tech seen the glowing converter. Allowed it too cool and performed a back pressure test.
I dont know the numbers but he said it was really bad.
They replaced converters and the other A\F sensor. Replaced both rear O2.
I was asked to go over it with him and provide insight on what to do next.
We warmed up the truck. Both LTFT 's at 0 . STFT B1 was sitching around nicely. STFT B2 was 0 .
I pulled up both rear o2's on screen , Only B1S2 was reacting to changes. B2S2 did nothing 0.02 volts. ( had no propane @ that location) did what we could.
The only code was P0051, returning right away after clearing and restarting. 1. So lets test for the Heater circuit code, B2S1.
Day Later. Its driven to my shop. I was told , He tested wires and it may need a Pcm. I performed the tests for the heater circuit, Tested the Black /white wire from the B2S1 plug too the pcm. Ohm and load test. Passed.
I put everything back together. Hook up the lab scope on B1 and B2 duty cycles on the Pcm.
B1 as you can see in the screen shot,( YELLOW Trace) is great. B2 Did nothing at all. Needs a pcm.
I thought Lets go a step farther, Im here already. I changed the Green trace over too the B2S2 signal. , That the pcm was showing 0.02 volts the day before.
Now Im sorry i didnt have a lot of time so I only got screen shots.
Back probing the pcm for B2S2 showed a good signal. I brought up the pcm in the background.
Then gave it a shot of Propane. What!? The pcm see's that almost 1.0 volt but not a 0.3 too .05 volts? On B2S2 . While it was reading 0.3-0.4 on B1S2.
Could this be High resistance in the pcm? Would/ should it cause a code later during OBD self tests?
Also That circuit that controls Pulse with modulation for the heater control. What was that device called?
Thoughts , Thanks for your time.
Did I find Two problems withthe PCM? was created by A.Bernier
This maybe confusing , I'll try to keep it clear.
2005 Toyota Tacoma 4.0 Vin U 4WD.
Was dropped at other garage, not running. They performed tune up and B1S1 due to a P0051 Heater circuit fault.
They did get the truck running, (not well) Tech seen the glowing converter. Allowed it too cool and performed a back pressure test.
I dont know the numbers but he said it was really bad.
They replaced converters and the other A\F sensor. Replaced both rear O2.
I was asked to go over it with him and provide insight on what to do next.
We warmed up the truck. Both LTFT 's at 0 . STFT B1 was sitching around nicely. STFT B2 was 0 .
I pulled up both rear o2's on screen , Only B1S2 was reacting to changes. B2S2 did nothing 0.02 volts. ( had no propane @ that location) did what we could.
The only code was P0051, returning right away after clearing and restarting. 1. So lets test for the Heater circuit code, B2S1.
Day Later. Its driven to my shop. I was told , He tested wires and it may need a Pcm. I performed the tests for the heater circuit, Tested the Black /white wire from the B2S1 plug too the pcm. Ohm and load test. Passed.
I put everything back together. Hook up the lab scope on B1 and B2 duty cycles on the Pcm.
B1 as you can see in the screen shot,( YELLOW Trace) is great. B2 Did nothing at all. Needs a pcm.
I thought Lets go a step farther, Im here already. I changed the Green trace over too the B2S2 signal. , That the pcm was showing 0.02 volts the day before.
Now Im sorry i didnt have a lot of time so I only got screen shots.
Back probing the pcm for B2S2 showed a good signal. I brought up the pcm in the background.
Then gave it a shot of Propane. What!? The pcm see's that almost 1.0 volt but not a 0.3 too .05 volts? On B2S2 . While it was reading 0.3-0.4 on B1S2.
Could this be High resistance in the pcm? Would/ should it cause a code later during OBD self tests?
Also That circuit that controls Pulse with modulation for the heater control. What was that device called?
Thoughts , Thanks for your time.
Last edit: 2 months 1 day ago by A.Bernier.
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