O2 sensor alarm

[Ted]

Hi all,

I had noticed that my O2 sensor connector has been broken and kept open( with reference to the ecu). But no alarm was given. I want to know whether any alarm is generated normally when O2 sensor is removed. 

[Davy]

1 hour ago, Ted said:

Hi all,

I had noticed that my O2 sensor connector has been broken and kept open( with reference to the ecu). But no alarm was given. I want to know whether any alarm is generated normally when O2 sensor is removed. 

The check engine light on the dashboard should be on and a diagnostic scan should reveal an error code. So yes, those are the "alarms". 

Does your check engine light turn on when your ignition is at the ON position and go off in a few seconds or after the engine is started? If not, your check engine indicator bulb may be burnt. 

Edited September 14, 2017 by Davy

[Rumesh88]

5 hours ago, Davy said:

The check engine light on the dashboard should be on and a diagnostic scan should reveal an error code. So yes, those are the "alarms". 

Does your check engine light turn on when your ignition is at the ON position and go off in a few seconds or after the engine is started? If not, your check engine indicator bulb may be burnt. 

Just to add a line to what Davy explained, sometimes our maka basses have a habit of bypassing the check engine light by connecting it in parallel with another indicator which comes on with the ignition key and disappears once the engine is started giving you the false impression that CEL is working. Keep that in mind too.

[Ted]

On 9/15/2017 at 3:28 AM, Davy said:

The check engine light on the dashboard should be on and a diagnostic scan should reveal an error code. So yes, those are the "alarms". 

Does your check engine light turn on when your ignition is at the ON position and go off in a few seconds or after the engine is started? If not, your check engine indicator bulb may be burnt. 

Yes... check engine is working..  unlike OBDII cars mine has just a code set identified by blinking counts of check engine light. (OBDI). So no scanner port in my car.  ECU and check engine seems working bcoz in test mode, check engine gives code 51 which is "AC is on" when I switch on my AC. 

Code 21 is fpr O2 sensor problem. If the ecu input from O2 sensor is normally open then for open connection it gives no alarm. I am going to short it and check. Will it be burn my ecu?

[Davy]

6 hours ago, Ted said:

Yes... check engine is working..  unlike OBDII cars mine has just a code set identified by blinking counts of check engine light. (OBDI). So no scanner port in my car.  ECU and check engine seems working bcoz in test mode, check engine gives code 51 which is "AC is on" when I switch on my AC. 

Code 21 is fpr O2 sensor problem. If the ecu input from O2 sensor is normally open then for open connection it gives no alarm. I am going to short it and check. Will it be burn my ecu?

How many wires does the connector have and what's the car we're talking about here?

Unlike hall effect sensors, the Oxygen sensor actually produces a small voltage between 100mV to 900mV or so. If one of the wires in your connector is a +12V line (some sensors are heated ones where a separate line heats up the sensor for cold starts), then yes, you have a risk of frying your ECU.

Did you note a sudden drop in fuel efficiency recently? Does your car idle normally?