Author Topic: Troubleshooting sensors and how to test  (Read 9015 times)

Offline Irish_Alley

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Troubleshooting sensors and how to test
« on: December 28, 2014, 04:18:29 AM »
Its not required for all sensors but some you need to check sensor readings by back probing the circuits at the ECM connectors.

Symptoms of a Defective C.T.S.
Check engine light is on
Bad gas mileage
Blowing black smoke
Running rich
Running lean

(Coolant Tempature Sensor) for the ECM on the intake
177       ohms @ 212 º F. or 100 º C.
241       ohms @ 194 º F. or   90 º C.
332       ohms @ 176 º F. or   80 º C.
467       ohms @ 158 º F. or   70 º C.
667       ohms @ 140 º F. or   60 º C.
973       ohms @ 122 º F. or   50 º C.
1188     ohms @ 113 º F. or   45 º C.
1459     ohms @ 104 º F. or   40 º C.
1802     ohms @   95 º F. or   35 º C.
2238     ohms @   86 º F. or   30 º C.
2796     ohms @   77 º F. or   25 º C.
3520     ohms @   68 º F. or   20 º C.
4450     ohms @   59 º F. or   15 º C.
5670     ohms @   50 º F. or   10 º C.
7280     ohms @   41 º F. or     5 º C.
9420     ohms @   32 º F. or     0 º C.
12300   ohms @   23 º F. or    -5 º C.
16180   ohms @   14 º F. or  -10 º C.
21450   ohms @     5 º F. or  -15 º C.
28680   ohms @   -4 º  F. or  -20 º C.
52700   ohms @  -22 º F. or  -30 º C.
100700 ohms @  -40 º F. or  -40 º C.

(Idle Air Control)
Symptoms of a Defective I.A.C.
 high or low idle
engine dies at idle
severe high idle

Terminals A to B should be 40 to 80 ohms
Terminals C to D should be 40 to 80 ohms
Terminals A to D should be infinite
Terminals B to C should be infinite

(Manifold Absolute Pressure)

Symptoms of a Defective MAP
The 'Check Engine' Light is On
Rough idle
A rich fuel condition, which may cause spark plug fouling
Detonation due to too much spark advance and a lean fuel ratio
Loss of power and/or fuel economy due to retarded timing and an excessively rich fuel ratio
A vacuum leak will reduce intake vacuum and cause the MAP sensor to indicate a higher than normal load on the engine. The computer will try to compensate by richening the fuel mixture and retarding timing -- which hurts fuel economy, performance and emissions.

Check the reference voltage supply at pin C of the MAP sensor (gray wire typically).
Measure voltage between pin A (ground) and Pin C (+5 V ref) with a DVM. It should be right around 5 Vdc.
With Key on engine off the MAP voltage (Pin B, light green wire typically) should read around 4.8 to 4.9 volts. If it reads the same as pin C the sensor is probably is history.
Also check ground reference pin A. With everything off, measure resistance between Pin A and electrical ground (stud next thermostat). It should be fractional ohms

                                                              Manifold Vacuum
kPA      0         10       20        30         40          50         60         70          80         90         100
Hg       0          2.9      5.9       8.9       11.8      14.8      17.7      20.7      23.7      26.7      29.6
Volts   4.9       4.4      3.8       3.3       2.7         2.2       1.7        1.1         0.6       0.3         0.3
         W.O.T.                                                                                                                        Idle

                                                              Manifold Pressure
kPa      100       90         80         70         60          50          40        30         20       10       0
Hg       29.6      26.6      23.7      20.7      17.7      14.8      11.8      8.9      5.9      2.9       0
Volts   4.9        4.4       3.8         3.3        2.7        2.2         1.7        1.1      0.6      0.3      0.3
         W.O.T.                                                                                                                        Idle

(Throttle Position Sensor)

Symptoms of a Defective TPS

The 'Check Engine' Light is On
Bucking and Jerking/Hesitation while Accelerating
Idle Surging
Sudden Stalling of the Engine
Sudden Surge in Speed While Driving on the Highway

Test between blue and black wire.
.5v idle to 5v WOT
the readings should gradualy change hitting no dead spots

Or you can test with a ohms meter
TPS Actuator Arm at rest:       Pins               Values (ohms)
                                               A to C       =       5.88k
                                               A to B       =       2.44k
                                               C to B       =       8.32k
Rotating the TPS Actuator Arm:                       At Rest      Rotated
                                               A to B       =       2.44k       8.26k
                                               C to B       =       8.32k       2.39k

(Oxygen Sensor)

Symptoms of a Defective 02
Poor fuel economy
Higher emissions

0.0 volts = Lean
1.0 volts = Rich

O2 sensor reading at the ECM to .450-.500mv when in open loop or the connector is disconnected.
ground the diagnostic connector and rev engine to 2000 rpm . The Check Engine light should flash once per second for closed loop operation and once every 1/2 second for open loop. It should start out in open loop and then change to closed loop and stay there.
If it flashes closed loop operation and then switches back to open loop operation for a few seconds. Check the O2 circuit for grounding out or poor connection. If that is OK then replace the o2 sensor.
if your getting a lean code this could point to a bad ground or poor conection

Knock sensor test
Parts store

the knock sensor produces its own electric currant. its very small but you can test for it. Set you tester to A/C probe the center of the sensor with the red lead and ground the black lead. now tap on the sensor it will produce 6-12 K hz

« Last Edit: December 30, 2018, 05:26:21 PM by Irish_Alley »
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