Trucks, Jeeps

Jeep Cherokee Sensor Testing (1987-1990)

Some sensors, which require a DRBII or similar machine test, are omitted from this article. The basis for these tests is the factory service manual procedures. Other years may use similar tests.

For these tests you will need a DVOM (Digital Volt-Ohm Meter) and your hands and eyes.

Throttle Position sensor tests (TPS)

There are two connectors from this sensor, a square one, which goes to the ECM, and a flat one that goes to the TCM. The square connector is what you will be using.

There is a small flap over the back side of the connector. Unclip the small catch and flip it up to expose the rubber seals where the wires go in. Insert you test lead probes here.

1) Turn ignition on (don’t start the vehicle) . Check throttle position sensor input voltage. Connect voltmeter negative lead to terminal "B" (M/T), or terminal "D" (A/T) of sensor connector. Connect voltmeter positive lead to terminal "A" (M/T and A/T) of sensor connector.

NOTE: On (automatic transmission) models, connector terminals are identified by letters molded into back of connector. On all models, do not disconnect TPS harness connector. Insert voltmeter test leads through back of wire harness connector. On some models, it may be necessary to remove throttle body from intake manifold to gain access to sensor wire harness.

2) Move and close throttle plate completely (M/T and A/T). Ensure throttle linkage contacts stop. Note voltmeter reading. Input voltage at terminals "B" and "A" (M/T), or terminals "A" and "D" (A/T) should be 5 volts.

3) Return throttle plate to closed throttle position (M/T and A/T). Check sensor output voltage. To do so, disconnect voltmeter positive lead from terminal "A" and connect it to terminal "C" (M/T), or terminal "B" (A/T).

4) Maintain throttle plate in closed position (M/T and A/T). Ensure throttle linkage contacts stop. Note voltmeter reading. Output voltage should be .8 volt (M/T), or 4.2 volts (A/T).

5) If output voltage is incorrect, loosen bottom sensor retaining screw and pivot sensor in adjustment slot for a coarse adjustment. Loosen top sensor retaining screw for fine adjustments. Tighten screws after adjustment.

I got everything within the good range on my tests, with the exception of the input voltage, which was 4.65VDC. I had a short circuit in the sensor grounds to TCM keep-alive memory wire earlier this year, I have repaired the damage, but I still think the ground wire may be damaged. This may be what is giving me the low input voltage.

MAP (Manifold Absolute Pressure) sensor test:

1) Inspect MAP sensor hoses and connections. Repair as necessary. With ignition on and engine off, test MAP sensor output voltage at connector terminal "B". (Marked on sensor body).

2) To verify wiring harness condition, test ECU terminal C-6 for same voltage described. Test MAP sensor supply voltage at sensor connector terminal "C" with ignition on.

3) Voltage should be 4.5-5.5 volts. Same voltage should also be at terminal C-14 of ECU wire harness connector. Using Diagnostic Tester (M.S. 1170), test MAP sensor ground circuit at terminal D-3 and terminal "A" of sensor connector.

4) Using an ohmmeter, test MAP sensor ground circuit at ECU connector between terminal D-3 of ECU connector and terminal B-11 with an ohmmeter.

5) If ohmmeter or diagnostic tester indicates an open circuit, inspect for a defective sensor ground connection, located on right side of cylinder block. If ground connection is good, ECU may need to be replaced.

My MAP tests out at the specs given here. So it is still functional.

MAT and CTS (Manifold Air Temperature and Coolant Temperature) Sensor Test:

1) Disconnect wire harness connector from MAT (or CTS) sensor. Test resistance of sensor with a high impedance digital ohmmeter. Resistance should be less than 1000 ohms with engine warm. Replace sensor if resistance is not within specified range. See TEMPERATURE-TO-RESISTANCE VALUES table.

The MAT is located on the intake manifold behind the Throttle Body. It it is threaded into the manifold.

The CTS is threaded in to the cylinder block just above the oil pan. It is the same size and shape as the MAT sensor. On most models, you can swap the two if need be. Just be aware that you will need to refill the cooling system if you remove the CTS from the block.

TEMPERATURE-TO-RESISTANCE VALUES (CTS & MAT SENSOR) TABLE

°F   °C (Approx.) Ohms
212   100 185
160   70 450
100   38 1600
70   20 3400
40   4 7500
20   -7 13,500
0   -18 25,000
-40   -40 100,700

Crank Position sensor test:

With the engine at normal operating temperature and the engine turned off. Unplug the CPS connector; it's two wires, up at the firewall. The connector itself may have a three-wire connector, with only two wires in it. Wire colors are: Purple w/white stripe and White w/black stripe. You know you have the right connector unplugged if you try to start the vehicle and it doesn't start.

Insert the test meter probes into the connector and read the resistance of the sensor. It should read between 125-275 Ohms. If it does not, than replacement is required. Mine is right at 175 ohms.

See other repairs at our Jeep Cherokee page

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