Malfunction Indicator Light (MIL) does not work?

[crhodes325]

I’m trying to diagnosis a new issue on my 2006 V6 Sonata . I plugged in my code scanner which gave back MIL Status as ON, but there was no Check Engine – Malfunction Indicator Light (MIL) lit up on the instrument cluster. It also showed that the EVAP, CAT and O2S was “Not Ready”. When I checked the codes, I had P0031, P0037, P0051 and P0057, all of which are tied to Low Heater Circuits in the O2 sensors. When I checked the cables under the hood, the lower O2 sensor cable closest to the firewall was stuck onto exhaust pipe. It easily pulled free but I tried clearing the codes but the same 4 codes remained. I checked the resistance across the heater control and ground circuit, all 4 O2 sensors were around 10 ohms.

There seems to be several issues:
1) Why doesn’t the instrument cluster register the MIL status as ON and display this Check Engine Light?
2) Why are the EVAP, CAT and O2 “Not Ready”, I’ve heard that these are sometimes tied to disconnecting the battery. I’ve put almost 3K miles on the vehicle since the battery change.
3) OBD Codes P0031, P0037, P0051, P0057, I would expect all O2 sensors to fail at once, is there a fuse or other control that needs to be replaced or reset?

I’m trying to get everything ready for emissions testing on this recently purchased 06 Sonata and I’m thinking these issues will cause it to fail.

[Mitchellv33]

Originally Posted by crhodes325

I’m trying to diagnosis a new issue on my 2006 V6 Sonata . I plugged in my code scanner which gave back MIL Status as ON, but there was no Check Engine – Malfunction Indicator Light (MIL) lit up on the instrument cluster. It also showed that the EVAP, CAT and O2S was “Not Ready”. When I checked the codes, I had P0031, P0037, P0051 and P0057, all of which are tied to Low Heater Circuits in the O2 sensors. When I checked the cables under the hood, the lower O2 sensor cable closest to the firewall was stuck onto exhaust pipe. It easily pulled free but I tried clearing the codes but the same 4 codes remained. I checked the resistance across the heater control and ground circuit, all 4 O2 sensors were around 10 ohms.

There seems to be several issues:
1) Why doesn’t the instrument cluster register the MIL status as ON and display this Check Engine Light?
2) Why are the EVAP, CAT and O2 “Not Ready”, I’ve heard that these are sometimes tied to disconnecting the battery. I’ve put almost 3K miles on the vehicle since the battery change.
3) OBD Codes P0031, P0037, P0051, P0057, I would expect all O2 sensors to fail at once, is there a fuse or other control that needs to be replaced or reset?

I’m trying to get everything ready for emissions testing on this recently purchased 06 Sonata and I’m thinking these issues will cause it to fail.

Do you have a good code reader, or a cheap ebay one? I have a cheap ebay one that will only diagnose MIL when MIL is 'ON' on the cluster. The computer however will store codes in the ECU. As far as I gather, when the ECU detects a fault in the system for more than 2 minutes, the MIL light will come on and stay on. It is possible that the computer see's a problem but not for long enough to turn the MIL light on, therefore storing the codes in the ECU. I had this problem with my old Accord. When I took it to my mechanic for some misc stuff, he told me I had a few codes stored in the ECU, one of which being something related to the secondary O2 sensor, however that sensor was fairly new and a genuine OEM part, installed at the dealership, so I didn't think anything of it at the time.

One thing you said I want to clarify, you said:

I would expect all O2 sensors to fail at once

This is unlikely. Infact very unlikely, especially with a V6 with 4 O2 sensors. Its typically advised that once one fails, depending on cost, that you replace any others as they could fail as well. The big word there being could.

I wouldn't worry to much about the car failing emissions because of heater circuit in the O2 sensors. If you were getting "fuel to lean/rich" then thats when I would worry.

I believe at this point that the MIL light isn't on for any of the following reasons:

1) Cheap scanner/program
2) ECU not detecting problem for more than 2 minutes
and as an absolute last guess:
3) Previous owner tampered with MIL light behind the cluster

Take the car and try for an emissions test, I believe it will pass. Only take it to a trusted mechanic, not shady chain shops/sketchy mechanics. Be sure to report back if it doesn't pass. Good luck.

[pare_john]

Does the MIL come on when the key is first set to on?

[crhodes325]

Originally Posted by pare_john

Does the MIL come on when the key is first set to on?

The MIL does not come on when the key is in the ignition and turned to the on position. The only lights that are eluminated on the instrument cluster are the Parking Brake, Oil, Battery and ESC Lights.

What lights should come on? ABS or Airbag light does not come on either.

To Mitchellv33's point, it is just a cheap code reader but P0031, 37, 51 and 57 are both active and pending errors. After a code erase, they are present upon restarting the vehicle.

And why would the EVAP, CAT and O2 be stuck in a "Not Ready" state? After putting 3,000 miles since last disconnecting the battery I would have expected the "Not Ready" state to reset back to "Ready".

[crhodes325]

Originally Posted by Mitchellv33

Do you have a good code reader, or a cheap ebay one? I have a cheap ebay one that will only diagnose MIL when MIL is 'ON' on the cluster. The computer however will store codes in the ECU. As far as I gather, when the ECU detects a fault in the system for more than 2 minutes, the MIL light will come on and stay on. It is possible that the computer see's a problem but not for long enough to turn the MIL light on, therefore storing the codes in the ECU. I had this problem with my old Accord. When I took it to my mechanic for some misc stuff, he told me I had a few codes stored in the ECU, one of which being something related to the secondary O2 sensor, however that sensor was fairly new and a genuine OEM part, installed at the dealership, so I didn't think anything of it at the time.

One thing you said I want to clarify, you said:



This is unlikely. Infact very unlikely, especially with a V6 with 4 O2 sensors. Its typically advised that once one fails, depending on cost, that you replace any others as they could fail as well. The big word there being could.

I wouldn't worry to much about the car failing emissions because of heater circuit in the O2 sensors. If you were getting "fuel to lean/rich" then thats when I would worry.

I believe at this point that the MIL light isn't on for any of the following reasons:

1) Cheap scanner/program
2) ECU not detecting problem for more than 2 minutes
and as an absolute last guess:
3) Previous owner tampered with MIL light behind the cluster

Take the car and try for an emissions test, I believe it will pass. Only take it to a trusted mechanic, not shady chain shops/sketchy mechanics. Be sure to report back if it doesn't pass. Good luck.

Sorry, typo on my part... I wouldn't expect all 4 to go bad at once. The fact that all four codes are active, leads me to believe their might be a short in the system or the ECU may have failed.

Yes, cheap code reader, no diagnostic features.