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Discussion Starter · #1 ·
This seems odd to me. I have a 2004, completely stock, 2.4 L base model extra-cab, with 160,000 miles. I occasionally receive an OBD code telling me of a small vacuum leak. Since it is small, and the severity is classified as 1 of 3, I have simply cleared the code several times. I have become familiar with the sound the OBD system makes when the reader is in operation. I have started to hear this sound now occasionally without an OBD reader attached. Is there something in the process of failing? What would you all do?
 

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Mambeau / Admin
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That's a new one on me ...

I don't think I've ever heard anyone claim the ECM makes any noise or sound when processing a code.

The only thing that's connected between the ECM and your reader is the OBD connector itself. There are no relays or other devices in the circuit that should / could be making a sound.

What sort of sound is it? Where does it seem to be coming from?

What code is it that you've been seeing and clearing? Maybe the sound you're hearing has something to do with the vacuum leak rather than the OBDII equipment.
 

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Discussion Starter · #3 ·
That's a new one on me ...

I don't think I've ever heard anyone claim the ECM makes any noise or sound when processing a code.

The only thing that's connected between the ECM and your reader is the OBD connector itself. There are no relays or other devices in the circuit that should / could be making a sound.

What sort of sound is it? Where does it seem to be coming from?

What code is it that you've been seeing and clearing? Maybe the sound you're hearing has something to do with the vacuum leak rather than the OBDII equipment.
__

Thank you for responding.

The OBD2 code that I see occasionally is: P0442. Evaporative Emissions System Leak Detected (small leak).
I initially replaced the gas cap with a Toyota Brand replacement.

With your description of the ECM / OBD2 connection, the ECM must not be the source of the noise. There must be some other equipment in the area that is causing the noise.

The sound is coming from the center of the dash, at a level just above and forward of the ash tray. In light of your explaination, my recognition of the noise must just be coincidence from when I first read the OBD2 error code.

The sound is a low, irregular, grinding noise (maybe a relay firing at a rate of a a few dozen times per second) that seems to be closer to the firewall than the ash tray / heater control area. It is not a loud sound.

Today, I ran the OBD2 reader again. I did not hear the sound at all. I tried with the engine off, with the engine warm at idle, and while driving. If, or when, I hear it again I will record the audio sound.

Thanks for your thoughts.
 

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Mambeau / Admin
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My first guess is that the sound you're hearing is coming from the emissions system components in the engine bay - for example, one of the vacuum valves clicking / buzzing.

I'm attaching the P0442 diagnostic section from the 2003 FSM (same as for 2004), along with a picture showing the locations of the emissions components in a 2RZ engine bay.

My guess is that the leakage / root cause is in the VSV for EVAP, the VSV for CCV, or one of the vacuum lines in the engine bay. Whatever's wrong is triggering the Vapor Pressure Sensor (in the rear; at the fuel tank) to signal the ECM there's leakage.

Hope this helps ...
 

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My first guess is that the sound you're hearing is coming from the emissions system components in the engine bay - for example, one of the vacuum valves clicking / buzzing.

I'm attaching the P0442 diagnostic section from the 2003 FSM (same as for 2004), along with a picture showing the locations of the emissions components in a 2RZ engine bay.

My guess is that the leakage / root cause is in the VSV for EVAP, the VSV for CCV, or one of the vacuum lines in the engine bay. Whatever's wrong is triggering the Vapor Pressure Sensor (in the rear; at the fuel tank) to signal the ECM there's leakage.

Hope this helps ...
We might deal with the possible vacuum leak on my friend's new Taco project. It has been throwing P0442 code and keep coming back. The truck is in the shop for the new rotor and nitto tires installation. Thanks for the diagram and the points to check for the leak.
 
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