Ch. 26

More documents

Recommendations

Info

602 CHAPTER 26 Four different types of test instruments can be used to test a pressure sensor: The Gavalier Convertible Story The owner of a Cavalier convertible stated to a service technician that the "check engine" (MlL) was on. The technician found a diagnostic trouble code (DTC) for a MAP sensor. The technician removed the hose at the MAP sensor and discovered that gasoline had accumulated in the sensor and dripped out of the hose as it was being removed. The technician replaced the MAP sensor and test drove the vehicle to confirm the repair. Almost at once the check engine light came on with the same MAP sensor code. After several hours of troubleshooting without success in determining the cause, the technician decided to start over again. Almost at once,the technician discovered that no vacuum was getting to the MAP sensor where a vacuum gauge was connected with a T fitting in the vacuum line to the MAP sensor. The vacuum port in the base of the throttle body injector was clogged with carbon. Afrer a thorough cleaning, and clearing the DTC, the Cavalier again performed properly and the check engine light did not come on again. The technician had assumed that if gasoline was able to reach the sensor through the vacuum hose,surely vacuum could reach the sensor. The technician learned to stop assuming when diagnosing a vehicle and concentrate more on testing the simple things first. Vacuum (in, Hg) Chrysler MAP Sensor Chart MAP Sensor Signal Voltage (V) 0.5 4.8 1.0 4.6 3.0 A1 1. A digital voltmeter with three test leads connected in series between the sensor and the wiring harness connector (see Figure 26-9) 2. A scope connected to the sensor output, power, and ground 3. A scan tool or a specific tool recommended by the vehicle manufacturer 4. A breakout box connected in series between the computer and the wiring harness connection(s). A typical breakout box inciudes test points at which pressure sensor values can be measured with a digital voltmeter (or frequency counter, if a frequency-type MAP sensor is being tested) til#THt Always check service literature for the exact testing procedures and specifications for the vehicle being tested. Use jumper wires, T-pins, or a breakout box to gain electrical access to the wiring to the pressure sensor. Most pressure sensors use three wires: 1. A 5-volt wire from the computer 2. A variable-signal wire back to the computer 3. A ground or reference low wire The procedure for testing the sensor Iows: as fol- 1. Turn the ignition on (engine off) 2. Measure the voltage (or frequency) of the sensor output 5.0 3.8 7.0 10 0 2.9 15.0 2.1 20.0 1.2 25.0 0.5 Testing the Map Sensor Most pressure sensors operate on 5 volts from the computer and return a signal (voltage or frequency) based on the pressure (vacuum) applied to the sensor. If a MAP sensor is being tested, make certain that the vacuum hose and hose frttings are sound and making a good, tight connection to a manifold vacuum source on the engine. Check the Hose A defective vacuum hose co a MAP sensor can cause a variety of driveability problems including poor fuel economy, hesitation, stalling, and rough idle. A small air leak (vacuum leak) around the hose can cause these symptoms and often set a trouble code in the vehicle cornputer. When working on a vehicle that uses a MAP sensor, make certain that the vacuum hose warels consistently downward on its route from the sensot- ro the source of manifold vacuum. Inspect the hose" e;oecially if another technician has previously replaced cr.e fucoryoriginal hose. lt should not be so long dlar c mgs down at any point. Condensed fuel and/or rrlo*Erre cayr become trapped in this low spot in the ircse 3:61 -*5g 2ll types of driveability problems and l'4A,p se".sw codes.
Canrputer Sensor Operation, Diagnosis, and Service 603 HARNESS CONNECTOR a @-@@ !B{j6Fe JUMPER WIRES Tr\ VACUUM PUMP 9*99: Figure 26-q A digital multimeter set to test a MAP sensor. (l) Connect the red meter lead to the V meter terminal and the black meter lead to the COM meter terminal. (2) Select DC volts. (3) Connect rhe rest leads to the sensor signal wire and the ground wire. (4) Select hertz (Hz) if testing a MAP sensor whose output is a varying frequency-otherwise keep it on DC vohs. (5) Read the change of frequency as the vacuum is applied to the sensor. Compare the vacuum reading and the frequency (or voltage) reading to the specifications. 3. Using a hand-operated vacuum pump (or other variable vacuum source), apply vacuum to the sensor A good pressure sensor should change voltage t or frequency) in relation to the applied vacuum. If the signal does not change or the values are out ofrange according to the manufacturers' specifications, the sensor must be replaced. F THROTTIE POSITION $EHSORS Most computer-equipped engines use a throttle position (TP) sensor to signal to the computer the position of the throttle. See Figure 26-10. The TP Figure 26*lS A typicalthrottle position (TP) sensor mounted on the throttle plate of this port-injected engine.
Page 1 and 2: Computer Sensor Operation, Diagnosi
Page 7: Computer Sensor Operation, Diagnosi
Page 11 and 12: i,cllipr-:;,*r' :i*ri:c,r iJ{:**-:1
Page 17 and 18: fomputer Sensor Operation, Diagnosi
Page 23 and 24: ?24-7 Select DC volts and turn the
Page 25 and 26: P25-l Oxygen sensors can be tested
Page 27 and 28: P25-l3 Push the MIN/MAX button to v

Ch. 26

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?