2000 Jeep Grand Cherokee Limited
6 cylinder (yes, a 6-cylinder limited)

My 4-speed automatic transmission went nuts on me today. Seems it forgot how to upshift to 2nd or higher. Tried manually moving the shifter to 2nd ... nothing. I took the RPMs up pretty high—almost redlining in 1st gear—but no upshift. I tried turning off the ignition and starting it again, but the same deal.

So, I drove the thing to a gas station in first gear ... 30 mph ... that was fun [I was on E of course]. I put in half a tank of gas and decided to drive home. Miraculously, it worked fine (although the check engine light was still on).

When I got home I did the old ignition trick to retrieve the error code. I came up with P0720. Here's what the research says:

P0720 (M) 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 (M) 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).

________________________

That's all well and good except the problem is that I have no idea what that means. Anybody experienced this before? Anybody know why there are two different descriptions for the same code? Any good suggestions on what I should do?

Thanks a ton.

Your transmission output sensor is bad or has a bad connection. There are two sensors on your model, an input speed sensor mounted to the front drivers side of the transmission and an output speed sensor mounted to the rear drivers side of the transmission.

2000 Jeep Grand Cherokee Limited
6 cylinder (yes, a 6-cylinder limited)

My 4-speed automatic transmission went nuts on me today. Seems it forgot how to upshift to 2nd or higher. Tried manually moving the shifter to 2nd ... nothing. I took the RPMs up pretty high—almost redlining in 1st gear—but no upshift. I tried turning off the ignition and starting it again, but the same deal.

So, I drove the thing to a gas station in first gear ... 30 mph ... that was fun [I was on E of course]. I put in half a tank of gas and decided to drive home. Miraculously, it worked fine (although the check engine light was still on).

When I got home I did the old ignition trick to retrieve the error code. I came up with P0720. Here's what the research says:

P0720 (M) 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 (M) 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).

________________________

That's all well and good except the problem is that I have no idea what that means. Anybody experienced this before? Anybody know why there are two different descriptions for the same code? Any good suggestions on what I should do?

Thanks a ton.

Thanks reekor ... I'll swap that out.

Any idea if my Jeep has the 42RE or 45RFE or 545RFE transmission?

I'm thinking it's probably the 45RFE

Any idea if my Jeep has the 42RE or 45RFE or 545RFE transmission?
All six cylinder 4.0 liter JGC motors for that year came with the 42RE.

As said above all 4.0L WJ's came with 42RE and 4.7L came with 45RF. In 2003 the 45RFE replaced the 45RF


Thanks reekor ... I'll swap that out.

Any idea if my Jeep has the 42RE or 45RFE or 545RFE transmission?

I'm thinking it's probably the 45RFE

As said above all 4.0L WJ's came with 42RE and 4.7L came with 45RF. In 2003 the 45RFE replaced the 45RF
Not exactly.All 4.0 WJs did come with 42RE transmissions,but 4.7s came with the 45RFE in 99 and 2000.2001 and later have the 545RFE.also the 42RE only has one speed sensor,the output.

I have a 99 GCL with the 4.7 and my trans output sensor went out. It felt like the brakes were being put on every few seconds. Went to the dealer and $45 later, 10 minutes work back like new. Scary.

I just checked alldata and the 42re does show one sensor for 1999 and two sensors for 2000 up. My hollander only shows the 45RFE 2003-04 for what its worth.

Not exactly.All 4.0 WJs did come with 42RE transmissions,but 4.7s came with the 45RFE in 99 and 2000.2001 and later have the 545RFE.also the 42RE only has one speed sensor,the output.

Update :::

I swapped the Speed Output Sensor ... $17 at Advance Auto ... problem solved!

Jeepman i have had the same problem, my tranny wouldnt get up to speed at 70 one day entering the on ramp to get on the interstate, it topped out around 40, i pulled over to the shoulder, put in park, put in drive, then it wouldnt move, i was revving it up pretty much, then i put in 2nd moved then back to drive and was moving to around 40 mph. made it to a gas station got towed home, did any check engine light come on for you? mine doesnt have a light to come on, i realize you said you did the old ignition trick thanks for help

Never mind i had a blonde moment, i re-read that and saw you said you did have a cel on