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Check Engine Light = No Overdrive?

My 1998 Cherokee has 160K miles on it. After I started it, the check engine light came on, which it does now and again because of low coolant or brake fluid. I ignored the light and went on my way, only to discover that the transmission would not shift into overdrive. The next time I started it, a couple hours later, the light was off and it shifted fine. It did this one other time since, same exact scenario. Trans fluid level and color is great. No other problems with the transmission. Any suggestions?

I think it is fairly clear that the car’s OBD system did detect a fault that interfered with proper functioning of the transmission. Maybe it was a transitory electronic problem or maybe it wasn’t.

I would suggest having the OBD system scanned for trouble codes before they are erased. If there is an electronic fault in the transmission’s controls, failure to fix it promptly can result in much more expensive mechanical repairs to the transmission.

Incidentally, your Check Engine Light (CEL) must work differently than all of the others with which I am familiar. I have never heard of a CEL lighting up because of low coolant level or low brake fluid level.

I am pretty sure that low coolant in the resevoir causes the check engine light to turn on. I have a bad heater core and don’t care to fix it ($$$). Every 3 months like clockwork, the light comes on, I fill the resevoir and the light goes off.

I don’t think the brake fluid turns the light on, I just replaced the master cylinder and the cap on the brand new fluid resevoir leaks! It never ends.

And it would seem reasonable that if the auto transmission cooling fluid line ran concurrently with the engine coolant line, I would think it IS worthwhile to have them dependent. Running in OD does generate more heat for the motor…and low brake fluid does mean you’re high speed braking when in OD may be compromised. So I agree with VDC and not assume it was a fault until other systems were checked and FIXED and it may not be a check engine light fault at all. Everything may be working as it should and it’s telling you to fix it.

So here is what I found after doing some extensive web research:

1)Neutral Safety Switch(NSS) malfunctioning (7 of 13 sources recommended this problem as the cause): very common problem for the Cherokees of this era (1996-2001). When not working it can cause the back-up lights to not work, check engine light to come on, and prevent shifting into overdrive. This is expensive ($300) to replace but can be cleaned for much less ($30). I have all of these symptoms. The diagnostic codes can be P0700 and P0705.

2)Speed Sensor malfunctioning. (3 of 13 sources recommended this problem as the cause): I didn’t find many details. This is a relatively inexpensive fix.

3)Throttle Position Switch (TPS) malfuntioning. (3 of 13 sources recommended this problem as the cause): I didn’t find many details. This is a relatively inexpensive fix.

Does anyone here have a recommendation? Thanks for your help, -Jeepheap

Since the CEL was associated with a malfunction of the transmission, it would seem to point toward #2, namely a Vehicle Speed Sensor (VSS). There is likely to be more than one on the car, so good diagnosis is important.

From afar, everything is merely guesswork. You really need to allow a qualified mechanic to diagnose the problem in person.

I confirmed the cost of the NSS tonight, it’s $240.00

Do you think it’s worth the moola?

No - what you seem to be doing is guessing. You need to get the thing scanned for error codes. You can blow and awful lot of time and money just guessing. The check engine light is not something you need to guess about. When it turns on an error code is stored in the computer. That error code will point you toward what you should be troubleshooting.

Major chain auto parts stores will read these for free. Call around and ask.

Dont guess, get the codes read and post them back here and we can go from there.

transman

That CEL (check engine light) is just a kid in class waving her hand trying to get you attention because she has the answer. You need to have the codes read. Some places will read them for FREE. Try Autozone or Advanced Auto Parts. Get the exact code (like P0123) not just their translation into English and post it back here.

“I confirmed the cost of the NSS tonight, it’s $240.00
Do you think it’s worth the moola?”

You seem determined to rely on long-distance guessing, and it seems that you are prepared to just start “throwing parts” at the problem. While you might get lucky, it is more likely that this approach will be more expensive than if you had a proper diagnosis done in the first place.

As we have all been telling you, it is time to have the car’s OBD system scanned for stored trouble codes.

That Low Coolant Problem Needs To Be Fixed. The Low Brake Fluid Problem Needs To Be Fixed.

I’m thinking that the low coolant is causing false coolant temperature readings (coolant sensor in air rather than coolant). The Jeep could be over-heating while indicating low coolant temperature.
I believe cars won’t lock up the torque converter or shift to overdrive until they’re up to operating temperature or if the ECM perceives that to be the case.

At any rate, the recurring low coolant can lead to additional damage or destruction of the engine and the low brake fluid can lead to the destruction of the whole vehicle or somebody else’s vehicle. Stop ignoring the light.

Of all the problems, the one about overdrive should be the least of your concerns. It’s too bad that it shifts into any transmission range. Fix it or park it.

CSA

I had the codes checked yesterday. They are P0700 (Check Transmission)
and P0705 (Transmission Range Sensor Circuit Malfunction (PRNDL Input)). From what I can gather, they point to the NSS.

Coolant problem is fixed. Had a leak in the lower radiator hose. Cheap and easy. Had them do a full flush and replace the T-stat while they were doing it.

Brake fluid only needed a new cap on the resevoir. Got it for free since they sold me a crappy one to begin with. (Just for you, I poured a little brake fluid on the ground anyway. HA!)

Thank you for your advise. -Jeepheap

Thanks, But What About This From Just About A Week Ago . . . ?

. . . “I am pretty sure that low coolant in the resevoir causes the check engine light to turn on. I have a bad heater core and don’t care to fix it ($$$). Every 3 months like clockwork, the light comes on, I fill the resevoir and the light goes off.

Is this fixed, too ? That problem will introduce air into the cooling system.

So, the CEL is off now ? The overdrive is fixed now ?

Am I not getting something, here ? You’re not flakey, right ?

CSA

Turns out the core is “restricted” but not leaking or evaporating coolant. It was just the leaking hose. I have to wear a thicker jacket on cold days.

CEL comes and goes with the shifting problem. Its happened once per week for 3 weeks. I was able to get to the shop to read the codes yesterday before they cleared. So normally, the light is off, but if it comes on, I immediately know I can’t drive on the highway because I don’t have overdrive. I posted the codes above.

Sorry, I Was Missing Some Information. Thanks.
CSA