I'm the new owner of a 89 turbo. I'm having a problem with the 02 sensor. The only code that's showing up is a 21 code. So I replaced the sensor with a new one. The check engine light still comes on as soon as the engine starts. I checked the voltage at the V1 and E1 terminals and get 0 volts.it's like there is no power going to the sensor. Not sure what else to check.
Code 21 Main oxygen sensor signal fault
- Thread starter noshine
- Start date
V1? Code 21 typically involves a loss of current through the sensor heater circuit. It's the only thing on the sensor that requires power. You should also clear codes and see what else is active because most O2 codes don't immediately get set. 21 does however.
Thanks for the reply! After I clear the code it pops up as soon as the motor starts. I was reading that you should you get voltage on terminal VF1 to E1 with the motor warmed up?? Oh by the way the old sensor wire was melted a little when I replaced it. Don't know if it messed something else up or not.
21 can be caused by other things but the heater circuit should be checked first.
http://www.cygnusx1.net/Supra/Library/TEWD/MK3/manual.aspx?S=Main&P=48
There are 3 wires on the O2 sensor. Two will be the same color, usually black. They're for the heater. Since the O2 sensor doesn't work unless it's hot the heater is used to get the engine into closed loop quickly and prevent it from falling out of closed loop when exhaust stream temperature is low. During idle for example.
One heater wire has 12 volts, the other is a ground controlled by the ECU. You can:
1) Check for 12 volts across the wires. If none, check which side (power or ground) is missing.
2) Measure current through them.
3) Disconnect the sensor and measure heater resistance.
4) Remove the sensor and connect it directly to the battery. It should very quickly become hot.
Bottom line: there needs to be appx 1 amp flowing through the heater to keep the ECU happy. If there is the O2 sensor itself should be checked:
http://www.cygnusx1.net/Supra/Library/TEWD/MK3/manual.aspx?S=Main&P=48
Course, in either case the sensor itself may be good but the wiring bad...
http://www.cygnusx1.net/Supra/Library/TEWD/MK3/manual.aspx?S=Main&P=48
There are 3 wires on the O2 sensor. Two will be the same color, usually black. They're for the heater. Since the O2 sensor doesn't work unless it's hot the heater is used to get the engine into closed loop quickly and prevent it from falling out of closed loop when exhaust stream temperature is low. During idle for example.
One heater wire has 12 volts, the other is a ground controlled by the ECU. You can:
1) Check for 12 volts across the wires. If none, check which side (power or ground) is missing.
2) Measure current through them.
3) Disconnect the sensor and measure heater resistance.
4) Remove the sensor and connect it directly to the battery. It should very quickly become hot.
Bottom line: there needs to be appx 1 amp flowing through the heater to keep the ECU happy. If there is the O2 sensor itself should be checked:
http://www.cygnusx1.net/Supra/Library/TEWD/MK3/manual.aspx?S=Main&P=48
Course, in either case the sensor itself may be good but the wiring bad...
OK I did some testing tonight. It has 12 volts between the two black wires. The problem seems to be with the 02 sensor plugged up there is no voltage between the wires. But when you check them one at a time there is 12 volts on each of the wires to ground. My meter doesn't do DC amps so can't check that yet. The sensor reads 5.3 ohms on the heater wires..oh if you go straight to the battery it does get hot.
Yep, with the sensor pluged in to the harness, you can read 12vdc from each black wire to the battery ground.But unplug the 02 sensor and only one of the black wires reads 12v and the other is the ground. If you check voltage on the two wires,while the sensor is pluged in there is NO voltage beween the two wires.. It like it a dead short with the sensor pluged up. but no fuses blow?
No. Fix it right. It seems like you have a potential wiring problem between the ECU HT pin and the black heater wire that reads 0V when the the sensor is unplugged. First step would be to measure continuity from the HT connector pin at the ECU and the corresponding pin on the O2 sensor.
Some of us are reading with a voracious appetite - so even if some aren't listening - some of us ARE; and storing the info for later use.jetjock;1942296 said:
Does the sensor get hot from the heater if it is removed from the manifold but still plugged in?