Jeep Cherokee (XJ): Diagnosis and testing

General diagnosis information

Shift points are controlled by the transmission control module (TCM). Before attempting repair, determine if a malfunction is electrical or mechanical.

The TCM used with the AW-4 transmission has a self-diagnostic program compatible with the DRBIII scan tool. The tester will identify faults in the electrical control system.

Diagnosis should begin with the Preliminary Inspection And Adjustment procedure. It is will help determine if a problem is mechanical or electrical.

The first procedure step is Initial Inspection and Adjustment.

Effects of incorrect fluid level

A low fluid level allows the pump to take in air along with the fluid. Air in the fluid will cause fluid pressures to be low and develop slower than normal.

Preliminary Diagnosis Check Procedure

If the transmission is overfilled, the gears churn the fluid into foam. This aerates the fluid and causing the same conditions occurring with a low level. In either case, air bubbles cause fluid overheating, oxidation and varnish buildup which interferes with valve, clutch and servo operation. Foaming also causes fluid expansion which can result in fluid overflow from the transmission vent or fill tube. Fluid overflow can easily be mistaken for a leak if inspection is not careful.

Causes of burnt fluid

Burnt, discolored fluid is a result of overheating which has two primary causes.

(1) A result of restricted fluid flow through the main and/or auxiliary cooler. This condition is usually the result of a faulty or improperly installed drainback valve, a damaged main cooler, or severe restrictions in the coolers and lines caused by debris or kinked lines.

(2) Heavy duty operation with a vehicle not properly equipped for this type of operation. Trailer towing or similar high load operation will overheat the transmission fluid if the vehicle is improperly equipped. Such vehicles should have an auxiliary transmission fluid cooler, a heavy duty cooling system, and the engine/axle ratio combination needed to handle heavy loads.

Fluid contamination

Transmission fluid contamination is generally a result of:

•  adding incorrect fluid
• failure to clean dipstick and fill tube when checking level
•  engine coolant entering the fluid
•  internal failure that generates debris
•  overheat that generates sludge (fluid breakdown)
•  failure to reverse flush cooler and lines after repair
•  failure to replace contaminated converter after repair

The use of non recommended fluids can result in transmission failure. The usual results are erratic shifts, slippage, abnormal wear and eventual failure due to fluid breakdown and sludge formation. Avoid this condition by using recommended fluids only.

The dipstick cap and fill tube should be wiped clean before checking fluid level. Dirt, grease and other foreign material on the cap and tube could fall into the tube if not removed beforehand. Take the time to wipe the cap and tube clean before withdrawing the dipstick.

Engine coolant in the transmission fluid is generally caused by a cooler malfunction. The only remedy is to replace the radiator as the cooler in the radiator is not a serviceable part. If coolant has circulated through the transmission for some time, an overhaul may also be necessary; especially if shift problems had developed.

The transmission cooler and lines should be reverse flushed whenever a malfunction generates sludge and/or debris. The torque converter should also be replaced at the same time.

Failure to flush the cooler and lines will result in recontamination. Flushing applies to auxiliary coolers as well. The torque converter should also be replaced whenever a failure generates sludge and debris. This is necessary because normal converter flushing procedures will not remove all contaminants.

Preliminary inspection and adjustment

(1) Check and adjust transmission shift cable if necessary.

(2) Verify transmission throttle cable operation.

Repair or replace cable if necessary.

(3) Check engine throttle operation. Operate accelerator pedal and observe injector throttle plate movement.

Adjust linkage if throttle plate does not reach wide open position.

(4) Check transmission fluid level when fluid is at normal operating temperature. Start engine. Shift transmission through all gear ranges then back to Neutral. Correct level is to Full or Add mark on dipstick with engine at curb idle speed.

(5) Check and adjust park/neutral position switch if necessary.

(6) Check throttle position sensor adjustment and operation. Adjust the sensor if necessary.

Manual shifting test

(1) This test determines if problem is related to mechanical or electrical component.

(2) Stop engine and disconnect transmission control module or module fuse.

(3) Road test vehicle. Shift transmission into each gear range. Transmission should operate as follows:

•  lock in Park
•  back up in Reverse
•  not move in Neutral
•  provide first gear only with shift lever in 1-2 position
•  operate in third gear only with shift lever in 3 position
•  operate in overdrive fourth gear in D position

(4) If transmission operates as described, proceed to next step. However, if forward gear ranges were difficult to distinguish (all feel the same), or vehicle would not back up, refer to diagnosis charts. Do not perform stall or time lag tests.

CAUTION: Do not over speed the engine during the next test step. Ease off the throttle and allow the vehicle to slow before downshifting.

(5) Continue road test. Manually downshift transmission from D to 3, and from 3 to 1-2 position.

Then manually upshift transmission through forward ranges again.

(6) If transmission operation is OK, perform stall, time lag and pressure tests. If transmission shifting problem is encountered, refer to diagnosis charts.

(7) If a problem still exists, continue testing with DRB scan tool.

Hydraulic pressure test

Pressure Test Procedure

(1) Connect pressure test gauge to test port on passenger side of transmission (Fig. 39). Use Adapter 7554 to connect gauge. Be sure test gauge has minimum capacity of 300 psi (2100 kPa).

(2) Be sure transmission fluid is at normal operating temperature.

(3) Apply parking brakes and block wheels.

WARNING: DO NOT ALLOW ANYONE TO STAND AT THE FRONT OR REAR OF THE VEHICLE WHILE PERFORMING THE FOLLOWING STEPS IN THE PRESSURE TEST.

(4) Check and adjust engine curb idle speed.

(5) Apply (and hold) service brakes.

Fig. 39 Pressure Test Gauge Connection

1 - PRESSURE GAUGE
2 - TEST PORT

(6) Shift transmission into D range and note line pressure with engine at curb idle speed. Pressure should be 61-to-70 psi (421-to-481 kPa).

(7) Press accelerator pedal to wide open throttle position and note line pressure. Pressure should be 173-to-209 psi (1196-to-1442 kPa).

CAUTION: Do not hold wide open throttle for more than 3-4 seconds at a time.

(8) Shift transmission into Reverse and note line pressure with engine at curb idle speed. Pressure should be 75-to-90 psi (519-to-618 kPa).

(9) Press accelerator to wide open throttle position and note line pressure in Reverse. Pressure should be 213-to-263 psi (1471-to-1814 kPa).

CAUTION: Do not hold wide open throttle for more than 4 seconds.

(10) If line pressure is not within specifications, adjust transmission throttle cable and repeat pressure test.

Pressure test analysis

If pressures in D and Reverse are higher than specified in test, check for the following: ² throttle cable loose, worn, binding or out of adjustment ² throttle valve, downshift plug, throttle cam, or primary regulator valve are sticking, worn or damaged If pressures in D and Reverse are lower than specified in test, check for following:

•  throttle cable loose, worn, binding or out of adjustment
•  throttle valve, downshift plug, or throttle cam sticking, worn or damaged
•  primary regulator valve sticking, worn, or damaged
•  oil pump gears or housing worn, or damaged
•  overdrive clutch worn, or damaged

If pressures are low in D range only, check for following:

•  forward clutch worn or damaged
•  fluid leakage in D range circuit (component seal and O-rings)

If pressures are low in Reverse only, check for following:

•  shift cable and manual valve out of adjustment
•  fluid leakage in reverse circuit (component seal and O-rings)
•  direct clutch worn or damaged
•  first/reverse brake worn or damaged

Time lag test

This test checks general condition of the overdrive clutch, forward clutch, rear clutch and first/reverse brake. Condition is indicated by the amount of time required for clutch/brake engagement with the engine at curb idle speed. Engagement time is measured for D and Reverse positions. A stop watch is recommended for test accuracy.

Test procedure

(1) Check and adjust transmission fluid level if necessary.

(2) Bring transmission to normal operating temperature.

(3) Apply parking brakes and turn off air conditioning unit.

(4) Shift transfer case into 2H range.

(5) Start engine and check curb idle speed. Adjust speed if necessary. Curb idle must be correct to ensure accurate test results.

(6) Shift transmission into Neutral and set stop watch.

(7) During following test steps, start stop watch as soon as shift lever reaches D and Reverse ranges.

(8) Shift transmission into D range and record time it takes for engagement. Repeat test two more times.

(9) Reset stop watch and shift transmission back to Neutral.

(10) Shift transmission into Reverse and record time it takes for engagement. Repeat test two more times.

(11) Engagement time in D range should be a maximum of 1.2 seconds. Engagement time for Reverse should be a maximum of 1.5 seconds.

Time lag test analysis

If engagement time is longer than specified for D range, check for the following:

•  shift cable misadjusted
•  line pressure low
•  forward clutch worn
•  overdrive clutch worn or damaged

If engagement time is longer than specified for Reverse, check for the following:

•  shift cable misadjusted
•  line pressure low
•  direct clutch worn
•  first/reverse brake worn
•  overdrive clutch worn or damaged

Service diagnosis

DIAGNOSIS TABLE

Transmission solenoid testing

Test solenoid resistance with an ohmmeter. Connect the ohmmeter leads to the solenoid mounting bracket and to the solenoid wire terminal (Fig. 40).

Solenoid resistance should be 11-15 ohms. Replace the solenoid if resistance is above or below the specified range.

Park/neutral position switch

SWITCH TESTING

Test switch continuity with an ohmmeter. Disconnect the switch and check continuity at the connector terminal positions and in the gear ranges indicated in Figure 3. Switch continuity should be as follows:

•  Continuity should exist between terminals B and C with the transmission in Park and Neutral only (Fig. 41).
•  Continuity should exist between terminals A and E with the transmission in Reverse (Fig. 41).
•  Continuity should exist between terminals A and G with the transmission in third gear (Fig. 41).
•  Continuity should exist between terminals A and H with the transmission in first and/or second gear (Fig. 41).

Fig. 40 Testing Transmission Valve Body Solenoid

1 - OHMMETER
2 - WIRE TERMINAL
3 - SOLENOID

• Continuity should not exist in D position

Fig. 41 Park/Neutral Position Switch Terminals And Testing

Gearshift cable

(1) The floor shifter lever and gate positions should be in alignment with all transmission PARK, NEUTRAL, and gear detent positions.

(2) Engine starts must be possible with floor shift lever in PARK or NEUTRAL gate positions only.

Engine starts must not be possible in any other gear position.

(3) With floor shift lever handle push-button not depressed and lever in: (a) PARK position-Apply forward force on center of handle and remove pressure. Engine starts must be possible.

(b) PARK position-Apply rearward force on center of handle and remove pressure. Engine starts must be possible.

(c) NEUTRAL position-Normal position. Engine starts must be possible.

(d) NEUTRAL position-Engine running and brakes applied, apply forward force on center of shift handle. Transmission shall not be able to shift from neutral to reverse.

Throttle valve cable

Transmission throttle valve cable adjustment is extremely important to proper operation. This adjustment positions the throttle valve, which controls shift speed, quality, and part-throttle downshift sensitivity.

If cable setting is too loose, early shifts and slippage between shifts may occur. If the setting is too tight, shifts may be delayed and part throttle downshifts may be very sensitive. Refer to the Adjustments section for the proper adjustment procedure.

Speed sensor testing

Test the speed sensor with an ohmmeter. Place the ohmmeter leads on the terminals in the sensor connector (Fig. 42).

Rotate the transmission output shaft and observe the ohmmeter needle. The needle should deflect indicating the switch is opening/closing as the rotor moves past the sensor (Fig. 42). Replace the sensor if the ohmmeter does not display any kind of reading.

Fig. 42 Speed Sensor Testing

1 - CONNECTOR
2 - OHMMETER
3 - SENSOR
4 - SENSOR SWITCH
5 - ROTOR

If a digital ohmmeter is being used, the sensor should generate an ohmmeter readout each time the switch opens and closes.

Flow testing transmission main cooler

Cooler flow is checked by measuring the amount of fluid flow through the cooler in a 20 second time period. The test is performed with the engine running and transmission in neutral. Fluid is then pumped through the cooler by the transmission oil pump.

(1) Disconnect cooler inlet line at transmission fitting.

(2) Securely attach hose to end of inlet line and position line in a one quart test container.

(3) Add extra quart of fluid to transmission.

(4) Use stopwatch to check flow test time.

(5) Shift transmission into neutral and set parking brake.

(6) Start and run engine at curb idle speed and immediately note cooler flow. Approximately one quart of fluid should flow into test container in 20 second period.

(7) If cooler flow is intermittent, flows less than one quart in 20 seconds, or does not flow at all, cooler is faulty and must be replaced.

Torque converter stator clutch inspection

(1) Insert Rotating Tool 7547 into converter hub and seat tool in one-way clutch (Fig. 43).

(2) Insert Stopper Tool 7548 in one converter hub notch and into outer race of rotating tool.

(3) Turn rotating tool clockwise. Converter clutch should rotate freely and smoothly. Less than 2.5 N·m (22 in. lbs.) of torque should be required to rotate clutch in clockwise direction.

(4) Turn rotating tool in counterclockwise direction.

Converter clutch should lock.

(5) Replace converter if clutch binds or will not lock.