I need to locate the heat sensor - 1999 Chevrolet Lumina

Four .
Heated Oxygen Sensor (HO2S Bank 1 Position 1)
Located in RH front pipe of the exhaust catalytic converter
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Engine Controls Connector End Views in Engine Controls
Heated Oxygen Sensor (HO2S Bank 1 Position 2)
Located in RH rear pipe of the exhaust catalytic converter
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Engine Controls Connector End Views in Engine Controls
Heated Oxygen Sensor (HO2S Bank 2 Position 1)
Located in LH front pipe of the exhaust catalytic converter
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Engine Controls Connector End Views in Engine Controls
Heated Oxygen Sensor (HO2S Bank 2 Position 2)
Located in LH rear pipe of the exhaust catalytic converter

Bank 1 is located towards the driver's side. Sensor 1 is located upstream just below the exhaust manifold.
EOBD II Error Code: P0134
Description:
Oxygen Sensor (O2S) 1, Bank 1/Heated Oxygen Sensor (HO2S) 1, Bank 1 - No Activity Detected
Possible Causes:
- Wiring.
- Signal wire between the Heated Oxygen sensor and ECM is disconnected.
- Heated Oxygen Sensor defective.
- ECM.

do you mean "coolant sensor" and witch engine

there are 4 o2 sensors on the nissan xterra . there is 2 o2 sensors in the exhaust pipe just after the exhaust manifold and there are 2 down under the truck

Fig. Component Location Chart-2000 MPV

1 PCM 2 Mass air flow (MAF)/intake air temperature (IAT) sensor 3 Throttle position (TP) sensor 4 Fuel tank pressure sensor 5 Engine coolant temperature (ECT) sensor 6 Crankshaft position (CKP) sensor 7 Camshaft position (CMP) sensor 8 Knock sensor 9 Heated oxygen sensor (HO2S) (front, LH) 10 Heated oxygen sensor (HO2S) (front, RH) 11 Heated oxygen sensor (HO2S) (rear, LH) 12 Heated oxygen sensor (HO2S) (rear, RH) 13 EGR boost sensor 14 Power steering pressure (PSP) switch 15 Main relay


Fig. Component Location Chart-2001 MPV

1 PCM 2 Mass air flow (MAF)/Intake air temperature (IAT) sensor 3 Throttle position (TP) sensor 4 Engine coolant temperature (ECT) sensor 5 Crankshaft position (CKP) sensor 6 Camshaft position (CMP) sensor 7 Knock sensor 8 Heated oxygen sensor (HO2S) (front, LH) 9 Heated oxygen sensor (HO2S) (front, RH) 10 Heated oxygen sensor (HO2S) (rear, LH)* 11 Heated oxygen sensor (HO2S) (rear, RH)* 12 EGR boost sensor


Fig. Component Location Chart- 2002-06 MPV

Hi:
The Number 1 Heated Oxygen sensor is located in front of the catalytic converter. You would need to get the car up in the air, and then disconnect the electrical connector, and possibly need a special socket to remove the sensor. Also remember to purchase and use Oxygen sensor safe anti sieze compound on the threads of the new sensor, if you do this your self

Fig. Heated Oxygen (HO2S) location (sensor 1)-2.4L engine



Fig. Heated Oxygen (HO2S) location (sensor 2)-2.4L engine



Fig. Heated Oxygen (HO2S) location (bank 1, sensor 2) (bank 2, sensor 2)-2.7L engine



Fig. Heated Oxygen (HO2S) location (bank 2, sensor 1)-2.7L engine

I hope help you with this (rated this help). Good luck.

try looking in general area of the thermostat

Heated Oxygen Sensor (HO2S) SPECIAL SERVICE TOOL(S) REQUIRED Description Tool Number Oxygen Sensor Wrench T94L-9472-A
Removal and Installation
NOTE: If excessive force is needed to remove heated oxygen sensor (HO2S) (9F472) , lubricate heated oxygen sensor with penetrating oil prior to removal.

1. Disconnect battery ground cable (14301) .

1. Disconnect heated oxygen sensors from engine control sensor wiring (12A581) .

1. Raise vehicle on hoist. Refer to Section 00-02 .

1. Remove heated oxygen sensors from dual converter Y pipe (5F250) using Oxygen Sensor Wrench T94L-9472-A.

1. To install, reverse Removal procedure. Tighten heated oxygen sensors to 36-46 Nm (26-34 lb-ft).
   
   

Oxygen sensors are located on the exhaust pipe in front and behind the catalytic convertor. There are more than one. If your check engine light is on, the code will tell you which sensor is faulty - I need that code to tell you the exact location.
Also really need to know the engine type to be more specific.
If your heat is not working there is probably a fault in the door mechanism that lets air pass over the heat exchanger under the dash. the switch is most likely at fault.