Engine Codes, Need Help

Hey, just got a '95 Cherokee and it's throwing a bunch of codes. Any help would be appreciated.

12-Direct battery input to PCM was disconnected within the last 50 key-on cycles.
17-Engine coolant temperature remains below normal operating temperatures during vehicle travel (thermostat).
51-Oxygen sensor signal input indicates lean air/fuel ratio condition during engine operation.
21-Neither rich nor lean condition detected from the oxygen sensor input.
or Oxygen sensor input voltage maintained above the normal operating range.
62-Unsuccessful attempt to update SRI (service reminder indicator) miles in the PCM EEPROM.
55-End

Some details, there is an aftermarket thermostat which opens at a lower temp. The gauge cluster was swapped to one with gauges instead of dummy lights. It has an aftermarket exhaust with high flow cat.

Does anyone think that going to the 24# Ford 5.0L Injectors will help the running lean code? Also if the O2 sensor is sending a high voltage does that correlate to running lean? In other words are codes 21 and 51 telling me the same thing? If anyone can give me some info on how to fix some/any of these I'd appreciate it.

Hallo
The O2 sensor gives a high voltage of 1 Volt when the mixture is rich.
When the engine is too cold, the coolant temp sensor gives to the ECU a signal too enrich the mixture.

wim

Unless you get the engine to the correct temp in the time allowed by the PCM you will always have those codes.
Correct that with the correct temp thermostat-195* and I bet your codes go away.

Wayne

I'll try that out. Any more suggestions? I'll probably be working on this Sunday, so I'll consider everything by then.

Thanks :cheers:

Update:

Okay, so I checked out the thermostat and it's a 195, so that shouldn't be the issue. I've been watching the gauge and it does come up to temp, about 210, very slowly. The guy I bought it from mentioned two things he did.

One, I believe he said he used a mixture very high in water and low in coolant in the summer and switched in the winter. Does this sound right to anyone?

Two, he said he uses a product called 'Water Wetter' which is supposed to drop your temp quite a bit. I've never used it but has anyone else heard that?

When I checked the t-stat, I had to replace some of the antifreeze/coolant, and noticed that the engine is getting up to temp a bit quicker. I haven't gotten a chance to change the O2 sensor yet, but a new development has happened. Since it's been colder in the morning the Cherokee has this hesitation, not at startup, but while accelerating. Also the CEL seems to come on mostly under highway driving when it hasn't warmed up all the way first.

Any new thoughts?

How slowly ? Time and distance.
It takes my 96, 10 min,or 3 miles to reach 210*,I can see the gauge drop when the stat opens and then rise back to 210*

At about 150* the engine will go into closed loop--and the O2 sensors will come into play.IIRC

I use water wetter and a 50/50 mix year round.
What are the codes now ? Maybe time to check the temp sensor for the ECU(in stat housing)for correct operation.

Or a new T-stat.The old one maybe letting water pass at too low a temp.

Wayne

Check the voltage at the gray wire in the o2 connector. Put a paperclip in the backside (aka backprobe) while it's still plugged into the main harness. It should read less than .5V, then above .5V, and so on- toggling rich/ lean very frequently while running, once the 02 heater has warmed up.

During normal driving, the temp sometimes never reaches 210*. If I let it sit at idle it'll reach right about 210* give or take 5*. When the needle goes through the 2 in the 210* it'll then drop to about 160* or so. I'll check the codes again but do I need to have them cleared so they'll be re-introduced and not just still in the ECU or if the problem's corrected will they clear themselves? Do you know what to check for with the temp sensor, I assume it outputs a voltage of some level.

I'll take a look at the O2 sensor output this weekend.

Thanks, I'll update again soon.

Replace the thermostat! The old one is bad. (195*f only)

Sounds like the thermostat is toast. Pull it out, put it in a pan of water with a thermometer, and boil that sucker.

Now here is the hard part--you have to sit and wait for the water to reach 195--and as we all know, A WATCHED POT NEVER BOILS!!!! (I am so funny!)

Seriously, it doesn't sound to me like it is functioning correctly.

Okay, so looks like you guys were right about the T-Stat being bad. I got a chance to switch it out last weekend and now my Cherokee warms up like a champ. The only problem is the 17 engine code is still showing up, not to mention the rest of them. One odd thing I noticed is that the engine codes have re-organized themselves and now the order is 12, 21, 21, 17, 51, 62, and 55.

Another observation that I didn't noticed before, which doesn't mean it wasn't happening, is that on cold mornings when I start her up, she'll idle a little high at first, which is typical, then the RPMs will suddenly drop to about 500 and the engine will struggle to stay on until the RPMs jump back to a normal running rate. Once the RPMs jump the engine light pops on. Now, once I've driven it around for a while this stops happening but the CEL will still come on from time to time.

By the looks of the codes I think I'm going to check out my O2 sensor and probably replace it, anyone agree? Any new suggestions?

Thanks

NEW UPDATE:

So I rolled under my Jeep to check the O2 sensor like was suggested in this thread and I reach up to touch the wires so I can follow them back to the harness, and the wires fall off the sensor. I took and look and have no clue how this thing was holding together but it was totally trashed, not to mention it looked original. So I went over to the local chain parts store picked up a new sensor, fought for a while to get the old one to break free and finally got the new one in. Afterwards, I took it for a drive and no CEL comes up so far.

The only question I have left is, how long will the codes that were showing stay in memory? I did the ignition on/off check and they're still there.

Thanks a lot everyone! Now I can get on to the fun work (lift, tires/wheel, etc.).
Sorch

Jot down all the radio freqs on the buttons.

Disconnect both cables from battery and hold cable ends together 30 seconds. Clean and vasoline battery posts and cable ends and reattach cables to battery. That should reset codes. (any new codes are real.)

Run - check for codes.

redo radio buttons.

It takes 40 clean starts for the Diagnostic Trouble Codes to be erased from the memory.
Even after that there will always be a 1-2 and a 5-5.

Wayne

orange said:

Jot down all the radio freqs on the buttons.

Disconnect both cables from battery and hold cable ends together 30 seconds. Clean and vasoline battery posts and cable ends and reattach cables to battery. That should reset codes. (any new codes are real.)

Run - check for codes.

redo radio buttons.

Click to expand...

Great plan - with one change. Don't have a brainfart and connect the battery terminals instead of the cables, unless you want to become part of the landscape. I usually do this by covering the positive battery post and touching the positive battery cable to the cleanest spot I can find on the frame (usually one of the radiator support crossbar bolts.)