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Discussion Starter #1
My alternator died and I drove home with a dying battery. I drove it until it died and I coasted it into the driveway. I replaced the alt and battery, no problem.

However, now I'm getting P0420, P0430, and c1201 codes.

Could I have damaged the cats by driving with a dead battery? Or, are the codes not related to the dead battery?

I have new O2 sensors ordered but not in yet.

Any advice would be appreciated.

2007 FJ with 135K miles, auto trans.
 

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You couldn't have driven very far with the dead battery obviously, but my guess is all the codes are related to the engine not sparking strong enough due to the battery losing charge which led to incomplete combustion. The O2 sensors probably threw the code because the cats weren't working efficiently due to incomplete combustion in the engine. IMO, all the codes should clear themselves but you could always clear them yourself and see if they come back.
 

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You couldn't have driven very far with the dead battery obviously, but my guess is all the codes are related to the engine not sparking strong enough due to the battery losing charge which led to incomplete combustion. The O2 sensors probably threw the code because the cats weren't working efficiently due to incomplete combustion in the engine. IMO, all the codes should clear themselves but you could always clear them yourself and see if they come back.
Yep. Clear the codes and see if they come back. If not, no prob.
 

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Driving with a dead battery would not have damaged the cats or the o2 sensors. If anything, the computer is still freaked out due to the unstable voltage that it received when the alternator died. I would disconnect the wiring harness to the computer for a good 15 minutes or so to ensure the codes are cleared. Then test the battery voltage to make sure that the new battery is at the proper voltage (12.6 volts I think). If it is lower than that, charge it up before you reconnect the computer.

And if all that fails, put some electric tape over the check engine light and all of your current and future engine problems are solved :)
 

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And if all that fails, put some electric tape over the check engine light and all of your current and future engine problems are solved
Genius!
 

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The major concern initially is the C1201 code, "Engine Control System Malfunction".

This indicates some problem with the engine control system, electronically a pretty complex system with many sensors, actuators, and a lot of wiring harness with many connectors. Simply running the battery down to the point where the engine stopped running should not have induced any permanent damage in any of the control system components, although if the engine ran excessively rich for the last 10-20 minutes of life it is possible that the air/fuel or oxygen sensors are fouled.

Questions:
1. At any point in this incident did you "jump start" the engine, or connect any type of auxiliary DC power supply to the vehicle?

2. Have you verified the engine-off battery voltage? It should be 12.6 - 12.9 volts measured at least 1/2 hour after engine shutdown.

3. Have you verified the battery charging voltage with the engine running at ~2K RPM, with all major electrical loads turned off? It should be between 13.2 to 14.8 volts.

These voltage measurements should be made with a good quality digital voltmeter, NOT an $8 Harbor Freight model. Make these measurements at the battery clamps, then also again at the battery posts.
 

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Discussion Starter #9 (Edited)
Never jump started and never connected any sort of power supply.

Also, I replaced the battery when I replaced the alt.

Voltages are all good and it is running well.

CEL is on and the three lights below the CEL are all on.

Check engine, VSC Trac, VSC off & slippery lights all have come on. Currently orange in colour
 

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What are you checking your codes with ? What codes do you have now? Have all the loops run? You say its running good and feels like plenty of power ?
 

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Discussion Starter #11
I'm checking and clearing codes with a BlueDriver. Still getting the same codes c1201, p0420, and p0430. It is running fine with plenty of power.
 

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Discussion Starter #12
Solved

I replaced both O2 sensors, cleared the codes, and they have not returned.

So, I guess driving with a dead battery can damage the O2 sensors.
 

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Discussion Starter #14
I just tested the old O2 sensors with an Ohm meter as per the service manual. Oddly it is not the heater circuit that failed. The measurement circuit showed an open circuit on both sensors.

I have no idea how this would occur from driving with a dead battery.
 

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I just tested the old O2 sensors with an Ohm meter as per the service manual. Oddly it is not the heater circuit that failed. The measurement circuit showed an open circuit on both sensors.

I have no idea how this would occur from driving with a dead battery.
You are misinterpreting the static resistance test.

An ohmmeter can be used to check the resistance of the heating element built into the sensor. You can detect opens, shorts and out-of-spec resistance values that would affect heater current draw and temperature.

You CANNOT verify the functionality of an air/fuel or oxygen sensor with an ohmmeter, only a shorted or partially shorted condition. Toyota "spec" for resistance is a minimum of 10K ohms, so infinite resistance ("open circuit" as indicated on an ohmmeter) is OK.

These sensors are very sophisticated devices, and the "span" of the output voltage, the linearity of the output voltage, and the response time are critical to proper operation. You cannot easily measure these characteristics with an ohmmeter or digital multimeter.

You need a diagnostic system, a lab oscilloscope, or an OBD plug-in module that monitors the vehicle's ECU and an app like Torque Pro that can display the output voltages of each sensor, and the commanded vs actual air/fuel ratios.
 

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Seems like you know more than Toyota and the service manual they print. The connector for the air fuel sensors are a 4 pin and on the sensor between pins 1 & 2 you should have 1.8 to 3.4 ohms and between pins 1 & 4you should 10kohms or higher. If the results are not as specified replace . For the O2 sensors between pins 1 & 2 you should have 11 to 16 ohms and between 1 and 4 you should have 10kohms or higher.
 

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Discussion Starter #18
I just replaced the O2 sensors (downstream of the cats).

The old O2 sensors tested as follows, both identical.

Pins 1 and 2 is 12.9 Ohms. (I assumed this to be the heating circuit)
Pins 1 and 4 is no connection or infinity. (I concluded this to be out of spec ???)

More driving with the FJ today and no codes, so, I'm calling it fixed.
 

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Seems like you know more than Toyota and the service manual they print. The connector for the air fuel sensors are a 4 pin and on the sensor between pins 1 & 2 you should have 1.8 to 3.4 ohms and between pins 1 & 4you should 10kohms or higher. If the results are not as specified replace . For the O2 sensors between pins 1 & 2 you should have 11 to 16 ohms and between 1 and 4 you should have 10kohms or higher.
pop -

You need to read a little further into the Toyota service manual to find the DETAILED procedure for actually testing the output levels of the air/fuel and O2 sensors (Section ES, Engine Control System, SFI System, pages ES-23 and ES-24 in my manual).

If you measure the resistance of the heating element with an ohmmeter, and find it to be 1.8 - 3.4 ohms (air/fuel sensor) or 11-16 ohms (O2 sensor) you are pretty well assured that the heating element is good and will function as designed.

If you measure the resistance of the zirconia sensing element and find it to be 10K ohms or greater, all you are verifying is that it is not grossly shorted. The ohmmeter test will tell you NOTHING about the functionality of the sensor: output voltage levels, output voltage linearity, and response time.


These characteristics must be measured with the sensor at operating temperature, immersed in the exhaust gas stream, and with the circuit properly "loaded".

The sensing element is a high-impedance voltage source, and you are looking at a total range of output voltage that only swings from about 0.1V to 0.9V, which is why you need a measuring instrument that can accurately resolve millivolts (thousandths of a volt).

If you have a high quality digital multimeter with an input impedance of 10 megohms or higher, you can monitor the voltage output of the sensor while the engine is running, looking for a continuous variation in output as the fuel-feedback system adjusts the mixture to keep it as close as possible to 14.7:1.

Denso, the manufacturer of Toyota's sensors, recommends the following procedure to help assess the sensors functionality:

Check the voltage signal.

1. Using a 10-megaohm digital voltmeter, connect the voltmeter's red probe to the sensor’s signal wire and the black probe to engine ground. (use back probe method, DO NOT pierce the wire)

2. Start the engine and let it idle for about two minutes while watching the digital reading on the voltmeter. It should be fixed for a short period at around 0.1 or 0.2 volts.

3. After two or three minutes, the voltage reading will begin to fluctuate between 0.1 and 0.9 volts. If the sensor takes four minutes or more to begin fluctuating, replace it.

4. Record the lowest and highest voltage reading from the voltmeter in any one-minute period. The voltage should fluctuate constantly between 0.1 and 0.9 volts.

5. Replace the oxygen sensor if the voltage:
a) Goes above this range,
b) Remains below 0.5 volts
c) Stays fixed at a particular voltage

6. Open and close the engine throttle with a quick motion. The sensor’s output voltage should go up and down accordingly."
 

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Have you ever actually worked on anything ? By your posts you have not. Toyota needs to hire you to re-do all their manuals. Toyota Manual tells how to test, ES-199 we are trying to clear codes ,engine ran fine no problems with the SFI .He tested, they were BAD, he replaced them and all codes cleared. The manual worked. Have a great day.
 
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