Transmission input & output speed sensors
Speed sensors location on the 45RFE / 545RFE transmission
The Input and Output Speed Sensors are two-wire magnetic pickup devices that generate AC signals as
rotation occurs. They are mounted in the left side of the transmission case and are considered primary
inputs to the Transmission Control Module (TCM).
Note:
The 42RE transmissions use a single sensor
(located on the overdrive gear case, over the park gear).
The 45RFE / 545RFE transmissions use two sensors, an input speed sensor and an output speed sensor.
Both are the same part number.
Operation:
The Input Speed Sensor provides information on how fast the input shaft is rotating. As the teeth of the
input clutch hub pass by the sensor coil, an AC voltage is generated and sent to the TCM. The TCM
interprets this information as input shaft rpm.
The Output Speed Sensor generates an AC signal in a similar fashion, though its coil is excited by rotation
of the rear planetary carrier lugs. The TCM interprets this information as output shaft rpm.
The TCM compares the input and output speed signals to determine the following:
• Transmission gear ratio
• Speed ratio error detection
• CVI calculation
The TCM also compares the input speed signal and the engine speed signal to determine
the following:
• Torque converter clutch slippage
• Torque converter element speed ratio
Sensor failure:
Failure of the Transmission Input Shaft Speed Sensor and/or the Output Shaft Speed Sensors are
somewhat common on early model WJ Grand Cherokees. Diagnostic Trouble codes that may be tripped
are:
P0500 - No vehicle speed sensor signal
P0720 - Low Output SPD Sensor RPM Above 15 MPH
The relationship between the Output Shaft Speed Sensor and vehicle speed is not within acceptable limits.
P0720 - Low Output SPD Sensor RPM Above 15 MPH
Output shaft speed is less than 60 rpm with vehicle speed above 15 mph
(4-speed auto. trans. only).
P0721-P0723 - Sensor circuit range, performance, no signal
Speed sensor removal
1. Raise vehicle.
2. Place a suitable fluid catch pan under the transmission.
3. Remove the wiring connector from the input speed sensor.
4. Remove the bolt holding the input speed sensor to the transmission case.
5. Remove the input speed sensor from the transmission case.
Speed sensor installation
1. Install the input speed sensor into the transmission case.
2. Install the bolt to hold the input speed sensor into the transmission case. Tighten the bolt to 105 in.lbs.
(11.9 N톗).
3. Install the wiring connector onto the input speed sensor
4. Verify the transmission fluid level. Add fluid as necessary.
5. Lower vehicle.
WJ speed sensors
Output speed sensor for 42RE transmission
(1999-2004)
Input speed sensor for 45RFE / 545RFE
transmission
P/N 4800879
(supercedes P/N
4412879)
P/N 4799061AB
List price:
$36.70
P/N 4799061AB
List price:
$36.70
(1999-2005)
Output speed sensor for 45RFE / 545RFE
transmission
List price:
$18.35
(1999-2005)
(Prices listed are for reference purposes only and may vary by dealer. Parts are not available from this web site.)
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Jeep Grand Cherokee Transmission Problems and Solutions
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www.thegearbox.org
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Jeep Grand Cherokees are considered as a fairly dependable vehicle by most people that have owned one.
They are great on the road as well as off-road.
There is only one major weakness about Jeep Grand Cherokees, and that is their automatic transmissions.
Jeep Grand Cherokee Transmissions are known to have problems earlier than other vehicles in the same
range.
In this article we will look at the most common problems that occur with the transmissions, and what you
need to do about it to get your Jeep back on the road again.
Jeep Grand Cherokee Transmission Fluid
Low Transmission Fluid
Low transmission fluid is one of the most common problems and the easiest to fix. That's why I always
check the transmission fluid first.
What you need to understand is that automatic transmission fluid (ATF) is responsible for 3 vital roles
within you Jeep Grand Cherokee. First it lubricates your transmission so that everything moves smoothly,
with minimal friction and minimal heat. Second, ATF supplies the transmission with the hydraulic pressure
it needs to work properly. Third, the transmission fluid cools the transmission through cooling lines.
When low ATF is the issue, it causes a wide range of Jeep Grand Cherokee Transmission Problems. It can
cause anything from gear slippage, bad or slow gear changes, overheating, and possibly complete
transmission failure.
So, if you're having Jeep Grand Cherokee transmission problems, the first step to take is to check your
transmission fluid level. You can have a mechanic do it, or you can do this by yourself by following these
steps.
1) Make sure your Grand Cherokee is on a level surface and apply the E-brake
(emergency brake).
2) Start it and let it warm up. You can see when it warms up by checking the temperature gauge. Keep it
started throughout this whole process.
3) Put your Jeep into neutral.
4) Open the hood and locate the transmission fluid dip stick.
5) Pull out the dipstick and examine the fluid on the tip of it closely. It should be transparent and clean
(no particles). If it's dark in color, smells burnt, or has particles in it, you definitely need a fluid change.
GO TO next section on Burnt or Dirty Transmission Fluid >>>
6) Wipe the dipstick clean with a lint free cloth and reinsert it.
7) Pull it out again to check the fluid level. It should be at the "Full" line on the dipstick. If it's full and
your fluid is clean, then replace your dipstick and you're done. Your ATF level is good.
8) If your fluid level is low, pour the proper ATF, through a funnel, into the dipstick tube, until it reaches
the "Full" line on your dipstick. Be careful not to overfill. You're done!
Simply filling your ATF fluid to the right levels may solve your Jeep Grand Cherokee transmission problems.
To find out, take your vehicle for a spin and see if it made a difference.
If you transmission fluid was low, this means you are leaking somewhere. This problem needs to be
addressed, because you will constantly need to check and top-off your transmission fluid.
Burnt or Dirty Transmission Fluid
This section is for those of you who, when checking your transmission fluid level, found it to be dark in
color, found it smelling burnt, and/or having particles in it.
While dark colored, burnt smelling, or dirty ATF can be a sign of a larger transmission problem, it can also
mean the transmission fluid has exceeded its useful life.
So don't go jumping to conclusions quite yet. Your transmission may still be ok, but you NEED to change
your ATF and filter(s) ASAP.
Burnt and dirty ATF can also indicate that your Jeep Grand Cherokee transmission is ran harder than it's
built for. This could mean that you towed heavy loads, raced, or off-roaded the vehicle rather than calm
street driving.
Old transmission fluid often has low lubrication qualities and coarse particles floating in it. If you don't
replace this fluid ASAP, It will speed up your Jeep Grand Cherokee transmission wear and could ruin an
otherwise good transmission.
Other Jeep Grand Cherokee Transmission Issues
Transmission Control Module and Sensors
Ok, so your transmission fluid is clean and filled to the proper level, but you still have Jeep Grand
Cherokee transmission problems. The next logical step (and next cheapest step) is to make sure your
transmission control module (TCM) and speed sensors are working properly.
With these parts not working correctly, your Grand Cherokee will fail to switch gears properly. It will either
switch gears too early, too late, or not at all. It can also have rough gear changes and sudden up-shifts or
down-shifts and/or grinding gears.
You see, the TCM and the speed sensors are what make your transmission "automatic". The TCM "tells"
your automatic transmission solenoids when to shift gears based on the rpm, input speed sensor, output
speed sensor, and a few others (vehicle speed sensor, wheel speed sensor, throttle position sensor, kick
down switch, brake light switch, etc). If any of these electronic components aren't working right, you will
have problems with gear shifting.
To solve this problem you need your vehicle scanned with an automotive diagnostic scan tool to figure out
if this is the issue and which sensor is failing. Now, I don't think anyone, who is not a mechanic, would
own one of these expensive tools (over $1000). So you will need to go to a mechanic to have your Jeep
Grand Cherokee scanned.
Before you go to the mechanic, call them up and ask if the automotive diagnostic scan tool they have can
scan your year of Jeep. If they have an older scanner, it may not be able to read the codes from a newer
model. It shouldn't cost you more than $30-$60 for the scan.
The scan should tell you if the sensors work and if they are taking a proper reading or not. If it happens to
be a sensor problem, simply purchase and replace them. Input and output speed sensors are the ones
that fail the most often. They will cost you about $30, so the total for this fix shouldn't cost you more than
$100 including the scan.
Transmission Internal Parts Failure
If the transmission fluid is good and your TCM and sensors are fine, but you still have Jeep Grand
Cherokee transmission problems, the issue is most likely inside the transmission.
Before we go any further though, you need to make sure the problem is actually the transmission and not
another part of the drive train. The drivetrain can have a few of the same symptoms as a failing
transmission. The transfer case, for instance, can grind gears, cause vibrations, or completely lock-up.
Same goes for the differentials. The drive shafts can make noise or vibrations if they are damaged or bent.
Watch the video clip below to see how a Grand Cherokee drivetrain works.
powered by Youtube
It would be bad if you rebuild or replace your transmission, only to find out it wasn't the issue in the first
place.
After you know for sure that the transmission is indeed the problem, you have two options. Either get
your Jeep Grand Cherokee transmission rebuilt, or have it replaced. I'm a firm believer in replacing your
transmission rather than rebuilding. Here is why:
Price: To purchase a low mileage used transmission for your Jeep Grand Cherokee it would cost about 1/3
the price of a transmission rebuild. The thing is, there is probably 10 times more work and expertise
required to rebuild rather than replace. When you rebuild, you need to take the transmission off the
vehicle, take it apart using very specialized tools, figure out what's wrong, order the part(s) (additional
cost and time), put it back together using very specialized tools, and finally put it back on your Jeep.
An average Joe will not be able to rebuild a transmission in his garage for sure and will need to hire a
transmission mechanic. But anyone with some technical skills and basic tools can do a transmission
replacement, and as a result saving labor costs.
Reliability: I strongly believe that low mileage used transmissions are more reliable than higher mileage
rebuilt transmissions. Why? Because old is old, and the rebuild may very well not hold too long. Your
transmission may require attention again in a few thousand miles.
I really hope this article on Jeep Grand Cherokee transmission problems helped you figure some things
out about your transmission problems.
If you are at that point that you need a replacement transmission for your Jeep Grand Cherokee, please
visit my website to see available quality used transmissions. Click Here: Jeep Grand Cherokee
Transmissions
You can find 1993 - 2012 grade A and grade B transmissions starting at about $300.
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