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WJ 1999 4.7 codes P0130, P0136, P1491, P0731 Please help

5K views 13 replies 2 participants last post by  jbanks25 
#1 ·
I bought a bit of a project limited GC a few days ago, and I'm just getting into what may be wrong with it. I know a little about the history of this guy in that it has a frequent stalling problem. Frequently the truck will die, and the gauges will die as well (Overhead display test will fail). The only fix is pulling the negative cable and then putting it back on. Then the truck fires right back up. I know the previous owners replaced the PCM, but I have no idea where it was sourced. It was programmed by a dealership though, but after I read the stickied post on this forum, I'm wondering if this could be the crank sensor failure problem.

As far as P0731 the transmission appears to be running on only 2 gears. No overdrive for sure, but I only feel it shift once. If I put the shifter in 1st it will run and never shift. Moving it to 2nd appears to do nothing, and moving it to drive then makes it shift up. OD on off has no effect.

Additionally sometimes the srs light will come on and then go off, which I attribute to a clockspring going bad.

Any thoughts on these issues would be helpful.
 
#2 · (Edited)
Welcome to the garage.
Does your jeep already have the hydraulic cooling fan?
Did you check fuse 16 (15A) in the PDC? It is feeding the hydraulic cooling fan module and the O2 sensor heaters.
That you loose the instruments and the EVIC point towards a problem with the PCI data bus, on which most of the electronic modules communicate on.This can be caused by a shorted bus to ground(close to/or 0V), shorted to a power source (can be any voltage above 2 V) or an electronic control module which is faulty and cuasing the bus voltage to rise to around 7.5V. Normal bus voltage should be around the 2 V.
Is there any connection regarding the stalling and the weather (rain)? A faulty crank sensor for sure can make the engine stall. A faulty crank sensor can bring down the 5V sensor feed, which also feeds cam sensor, TPS and MAP sensors. Seems that the PCM in that case can short out the PCI data bus.
The P0731 means an incorrect gear ratio in 1st gear. This normally means that it is slipping in 1st gear (so ratio between input and output is not within expected range). Most probably the TCM will put the transmission in 3rd gear (limp mode) when in D, or 2nd gear with shift lever in 1st or 2nd. This should normally reset after ignition off/on, but with the fault active, it will return into limp mode as soon as you start driving again.
 
#3 ·
thanks for the reply, I really appreciate it. FUSE 16 (O2 10amp) looks good. I was really hoping you were going to say internal crank short, but I was afraid it would be a sorted write house chase... Any common places to look? I just took possession of the jeep, so I have no idea if train is a factor yet. I grabbed a lot of the bundled words and shook/tapped then quote a bit and couldn't get it to stall today. 40 miles without incident.

as for the transmission, that's bad news. I was hoping for a sensor. I for sure have 2 forward gears at all times though. Is that still how limp mode would operate?
 
#5 · (Edited)
According the jeep service manual fuse 16 should be a 15A, but maybe it has a lower value on your jeep because it doesn´t have the hydraulic cooling fan.
The short can well be inside the crank sensor, they used to start giving problems when getting hot. Probably a good point to start with this sensor, it sits right above the starter and the starter must be removed to get access to it. Mopar sensors seem to perform better then aftermarket stuff.
Does the transmission always shifts twice when in D? Its normal when in limp mode that D = 3 rd gear and 1st/2nd is 2nd gear. But in D it should not shift when in limp mode. If it still shifts, its not in limp mode.
Did you reset the fault codes and see if they came back?
 
#6 ·
Crap, cursed myself. I just went out to start it and it wouldn't. My code reader could still connect to the ECU though. Only reading the transmission code at that point though. Battery is now disconnected so I can start it later.

When I am in Drive I always have 2 forward gears. So not sure where that leaves my Trans, but I guess not in limp.
 
#7 ·
Yeah, it must be really grumpy now because it won't start. I htink hooking my scanner up may have ticked it off. It's funny, with key in the on position dash lights up, but no gages respond. If I try the code reader then, it can connect (I can actually hear it generating interference over the radio as it connect which seems strange) and it can pull engine rpm at 0 and TPS at 1.9 in the live data.
 
#8 ·
TPS at 1.9% is not normal, at least on my jeep it sits around the 12%. Could be that the crank sensor is pulling down the 5V for the sensor feed. You could measure the voltage at the TPS, or just disconnect the crank sensor and see if the TPS reading comes back to a value above the 10%. If so, then you are sure the crank sensor is faulty. If you want to measure on the TPS, then the 5V feed is on pin 1 of the TPS connector.
I would not worry about the transmission problem at this point, but first solve the engine problem, because you never know if the engine problem is causing the transmission problem.
 
#9 ·
Question for you guys, do you have any idea if this information is correct? (I found it on another forum)

Fuse Number 10 is dedicated to Transmission range sensor, duty cycle evap/purge solenoid, radiator fan relay, a/c clutch relay, o2 sensor up/downstream relays, back up lamp switch

Since I'm throwing codes with the fan, O2 sensors and transmission range if this is correct info I feel like I've got a pretty clear indication of what circuit I need to try to trace. Too big a coincidence that all the codes come form one place if this is true.
 
#11 · (Edited)
Fuse Number 10 is dedicated to Transmission range sensor, duty cycle evap/purge solenoid, radiator fan relay, a/c clutch relay, o2 sensor up/downstream relays, back up lamp switch
I don´t know where you have red this, but it is not true. Fuse 10 in the PDC i only see for the rad cooling fan (4.0L). My schematic (99-00MY) doesn´t show the electric fan for the 4.7L.
All the other components you mentioned are fed via other fuses:
EVAP/purge solenoid- fuse 21 on Junction block (JB)
TRS gets power from fuses 12 and 31 on the JB
AC compressor from fuse 21 on JB and fuse 21 in PDC under the hood
O2 sensors fed via fuse 16 in PDC
Back-up lights from fuse 20 on JB

So there is no connection in the power feed for the systems you have mentioned.
 
#10 ·
Also, another interesting situation. If I plug in my scanner and erase the codes (Key on but not started) Al the codes will go away, but I will kill the Jeep. Usually if it has it's starting problem you can pull the negative cable and put it right back. After erasing codes, pulling the cable doesn't help right away. Yesterday I had to leave it overnight.
 
#12 ·
The jeep will not start and the instruments don´t work as well? Did you already try a new crank sensor? If the crank sensor shorts out, the engine will not start and hearing from others the PCM will not give any output for the instruments. If checking the wires for shaving didn´t reveil anything, i would start with a new crank sensor and see how it behaves then.
 
#13 ·
I think it actually may be bad PCM connections. I got the Jeep nice and hot today and then moved the radiator overflow out of the way. I then jiggled each of the connectors at the ECU. The vehicle stalled out immediately when handling the far left one. I pulled the ECU and looked at it and looks like the one that the owners I got it from put in was a Mopar reman unit sourced from a junkyard. I know after they swapped it in the Jeep still didn't run right, so I suspect they cheaped out and got burnt. They gave up on it right after that.
 
#14 ·
Also, I found some documentation that says I am in limp mode, but it's a form of limp mode caused by computer communications failure.

* Logical shutdown with recovery -- The TCM operates the transmission at a steady preset pressure value and uses 1st and 3rd gears only while in Drive. The transmission will resume normal operation if the problem goes away.
 
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