Its not required for all sensors but some you need to check sensor readings by back probing the circuits at the ECM connectors.
C.T.S.
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
Testing
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.
I.A.C.
(Idle Air Control)
Symptoms of a Defective I.A.C.
high or low idle
engine dies at idle
severe high idle
Testing
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
M.A.P.
(Manifold Absolute Pressure)
Symptoms of a Defective MAP
The 'Check Engine' Light is On
Surging
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.
Testing
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
T.P.S.
(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
Testing
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
02
(Oxygen Sensor)
Symptoms of a Defective 02
Poor fuel economy
Higher emissions
Stalling-Hesitation
Test
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
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