主题：【原创】独角兽的修车自学笔记 -- 独角兽

1）Code Scan （重复多次，切记读code时关掉风扇）

“3 codes found: P0115，P0401, P0401 (pending，在规定时间内错误出现次数不够)”

“MIL on”

“Monior viewed: 0 incomplete, 8 ready （计算机记录了足够多的数据）( Misfire, Fuel, Comp, Catlyst, Evap, O2 Snsr, O2 Htr, EGR)”

2) Repair Manual Study:

说的太专业，维修貌似基于toyota hand－held tester tool. 针对问题似乎太严重，engine红灯而不是黄灯。但是学习了基本概念，电路组成，及零件位置（图画的不好，实物的确认还没有完全肯定）

3）google 关键词：

得到若干答案，觉得最靠谱好用的是下面这个

Engine coolant Temperature sensor (DCT Code : P0115)

Check Engine Cooling Sytem and radiator circuit for any possible leakage.

Inspect Radiator and hoses connection for leaks. Keep checking level of radiator coolant very often. If there is no leak...

A thermistor built into the engine coolant temp. sensor changes the resistance value according to the engine

coolant temp.

DTC - P0115 Open or short in engine coolant temp. sensor circuit

-Open or short in engine coolant temp. sensor circuit

-Engine coolant temp. sensor

Follow these steps.

(a) Disconnect the engine coolant temperature sensor connector.

(b) Connect the terminals 1 with 2 of the engine coolant temperature

sensor connector. Measure the resistance between terminal 1 and 2. check for open circuit or short circuit. Ideally it should read between 2.0 Kohms to 3.0 Kohms.

(c) Turn the ignition switch ON. Start the vehicle.

(d) Measure the resistance between terminal 1 and 2. As the coolant temperature starts rising up, the resistance starts falling down. At 180 deg C it should read approximately 0.2 Kohms, depends on make.

If the ECM detects the DTC P0115, it operates fail safe function in which the engine coolant temperature is assumed to be 80_C (176_F).

EGR – Exhaust Gas Recycle (DTC Code: 71 or P0401)

EGR system reduces NOx output by re-circulating portion of exhaust gases with normal air-to-fuel charge in the engine. EGR Flow is higher while cruising and mid-range acceleration when typical combustion temperature is very high. At lower speed and light load condition lower EGR flow is required. No EGR flow is required while idling or engine warm-up. There are four major components in EGR system, EGR Valve, EGR Vacuum Modulator, VSV: ECU controlled Vacuum Switching Valve and EGR Gas Temperature Sensors plus piping. With the age of the vehicle, EGR system problem is very common.

Use this routine:

-Remove the EGR Vacuum Modulator from the holding clamp and open the top cap. Inspect and replace the filter if required. Diesel (without any rust inhibitor additives or contents) can be used for removal of carbon deposits in the piping.

-Remove the EGR Valve from the mount. Remove the EGR inlet and outlet pipes from the exhaust manifold and the intake manifold. Blow air in inlet port and check for external and internal leaks. Inspect and replace the gasket if required. Inspect the manifold EGR ports and the EGR inlet and outlet pipes for a blockage caused by excessive deposits, casting flashing or other damage. Diesel (without any rust inhibitor additives or contents) can be used for removal of carbon deposits in the piping (A heavy guitar string on a drill motor works real good for running thru the manifold passage to open up the port). Then re-install the EGR and road-test again and also try cruise control at various speeds. If the light doesn't come on, you know that was the problem.

-Check EGR Temperature Sensor.

- Check and clean inlet and out let ports plus electrical connector of EGR VSV. ECU uses three signals to control the operation of EGR VSV switch --- distributor signal, coolant temperature signal and vacuum pressure signal. So after carrying out EGR system maintenance, you should service clean up for distributor cap and clan up electrical contacts of distributor, engine coolant temp sensor and vacuum sensors.

Again, with the age of the vehicle, this is very common