turn off Check engine light

[jdsalas]

I just finished replacing a bad cps for a 96 Jeep Cheroke with inline 6, 4.0L engine, autotrans 4wd . and I can't get the chack engine light to turn off. I disconnected the battery but still on. I checked for any codes and I only get 12 (50 to 100 starts to re-learn car performance) and 55 (to end code sequence). Jeep works fine too.

[JDPascal]

Most times I've found that I needed to leave it disconnected for at least 5 minutes to clear things.

JD

[sector95]

You indicate you've scanned for codes; do you have a scanning tool? If you do, then it usually has a function to reset fault codes. If you went to the local AutoZone to download the codes, then have them do the reset for you. Barring that, I would do the battery disconnect again then try and start the engine, operate any electrical acccessories and let the vehicle sit overnight. The idea is to discharge any short-term holding capacitors used to provide voltage to the computer's memory.

mike

[jdsalas]

Originally Posted by sector95

You indicate you've scanned for codes; do you have a scanning tool? If you do, then it usually has a function to reset fault codes. If you went to the local AutoZone to download the codes, then have them do the reset for you. Barring that, I would do the battery disconnect again then try and start the engine, operate any electrical acccessories and let the vehicle sit overnight. The idea is to discharge any short-term holding capacitors used to provide voltage to the computer's memory.

mike

Thanks I'll remember that next time but I'm turning mine in to get a new muffler welded on so I asked the mech if he could reset the light too. Oh.... I did the ignition on off sequence, I don't have a scan tool.

[gregory914]

My mechanic just told me that if you clear the codes, it takes three "3" driving sessions to re-set the computer so you don't get any non-reset codes. And that only works if you cleared them with a Scan Tool, you can't clear them otherwise.

Just an FYI I learned a couple of hours ago.

[axekick]

If you disconnect the battery cables and touch them together for four seconds the light will turn off.

[jdsalas]

Well I just got informed by the mechanic that the light won't turn off because of a code "P1492" battery temp sensor voltage to high. He said he checked it out and couldn't find anything wrong and he will talk to a tech to find the problem. So I'm driving around (without any problems) until he can fix it or I can figure it out. Which leads me to the next question... where is the battery temp sensor? and why would it have to high of a voltage and how can I repair it. One of the things that the Mechanic checked is the alternator and the battery itself and there are both O.K. Thx for any help.

[Saudade]

Don't know about your year but the 2000 fsm says:

BATTERY TEMPERATURE SENSOR
The battery temperature sensor is located under
vehicle battery (Fig. 5) and is attached to a mounting
hole on battery tray.

[jdsalas]

Originally Posted by Saudade

Don't know about your year but the 2000 fsm says:

BATTERY TEMPERATURE SENSOR
The battery temperature sensor is located under
vehicle battery (Fig. 5) and is attached to a mounting
hole on battery tray.

The manual I have (Chilton) doesn't contain information on how to test repair or replace. I appreciate any info on what to do with battery sensor voltage is to high. THX

[JDPascal]

Originally Posted by jdsalas

The manual I have (Chilton) doesn't contain information on how to test repair or replace. I appreciate any info on what to do with battery sensor voltage is to high. THX

The battery temp sensor allows the voltage regulator to increase the chargeing rate/voltage for lower temperatures and reduce them for high temps.

The battery temp sensor receives a 5 volt signal from the PCM and is grounded back at another common sensor ground terminal on the PCM so the battery won't and alternator won't have a direct effect on it's operation.

The only things that I know of that would make the voltage high is an open sensor, power side wire off or a disconnected ground wire somewhere near the sensor or high resistance anywhere in that run of the circuit.

I don't have the diagram for the cherokee but the grand cherk diagram shows a red/yel wire as being the power and a blk/blu wire being the ground side (maybe yours is the same?). If the battery temp sensor is the only problem showing up, that tells me that the problem is somewhere between the power terminal at the PCM and the first ground junction after the sensor.

Check the connectors at the sensor and at the PCM. Could have had acid from battery cause corosion on the sensor connector - or something like that.

The ground junction after the sensor should be close to the sensor. Just follow the wire into the harness.

If you check voltages, use a digital voltmeter with 10 megaohms impedence.

With the connector on the sensor, there should be 0 volts on the ground side. The voltage on the power side will vary with temperature but less than 5v.

If the connections are good, the power side at 5v or even slightly above and the ground voltage is 0v then the sensor has failed open and needs replacing, disconnect it and check it with an ohm meter. Infinity (1) on the meter means open - 0 means shorted.

hope this wasn't too involved for what you wanted.....

JD

[jdsalas]

Thank You everybody for your help. The Mech found the sensor and found that it wasn't connected good. He cleaned the connections and plugged it back up then the check engine light turned off. Again THANKS FOR ALL THE HELP. I have one more question... How much is the cheapest scanner and where can I get one. I hope it's not that expensive as the ones I have encountered already ($499.00 ~ $2,500.00). again thx for your assistance.

[Saudade]

You can find cheap scanners on eBay. The cheaper ones (less than $50), give you the codes but you have to look them up in a book. Mkae sure you get the right one for your manufacturer. The more expensive ones can tell you the problem on screen. Even better ones can allow you to run real times diagniostics, get Dyno data, even graph results.

I opted for the cheap one.

[jdsalas]

THX I'll Chk there