Jeep Cherokee OBD

'98 Cherokee Sport onboard computer spontaneously resets which prevents me from being able to connect to the emissions test equipment required to renew license tag. My mechanic has checked out electrical system and emissions values, and all are OK. Just can’t get the onboard computer to reset and STAY reset! If this isn’t remedied the vehicle won’t be eligible to be driven because of expired tags. My mechanic says maybe replace the computer ($800), but it may not solve the problem. Any advice?? -Joe

have you tried removing it, cleaning the connections then plugging it back in?

Here’s a used one that might work:

I’m not familiar with your truck, but it seems to be that there are two ways to loose the codes. First is that there is a nonvolatile memory that stores the OBD-II codes and te memory chip is shot. You probably can’t buy memory alone, so you have to replace the ECM. The second is the ECM uses volatile memory (less likely) and the power drops to the ECM and the memory is erased. The used unit on eBay Motors is $170 and it might be worth a shot. I think that replacement is easy enough that you can do it yourself, as long as you can get to it without removing too much stuff. You just need to keep track of where the connectors are disconnected so that you can reconnect the properly. You might tag them so that you know where they go in case you are interrupted for some reason.

Yes, I have cleaned all connectors. No luck. Thanks, though.

You should hit the junkyards; they have stacks of computers. Somebody has to have one for a Cherokee that will work. Prices can’t be bad everywhere. If you call around, you might get the price down a bit.

This is a long shot, but what is the condition of the battery? Recently the battery on my 2000 Blazer had been discharged to 12.1 volts (~25% charge). The voltage was low enough to cause the ECM/PCM to act up, i.e. high idle and the torque converter lockup not engaging. Once the battey was fully charged (12.6 volts) using a Battery Tender the truck ran normally. It’s predecessor, a 95 Dakota (OBD-I) also experienced driveability problems with a bad battery (10.1 volts).

Ed B.

If your mechanic has a digital voltmeter, and knows how to use it, have him to use the wiring diagram to locate ALL the battery power wires at the engine computer electrical connectors and take readings, with engine running, and engine not running. The voltages should be within a fraction of a volt of the battery voltage. All the grounds from the engine computer should be checked, also.
The power supply voltages at the engine computer should be within a fraction of a volt of the battery (or, alternator output) voltage. The grounds should be within a fraction of an ohm of earth (body) ground. If not, repairs to wires/connections are in order.

More good advice from Hellokit again.

I would also make sure that the continuous voltage to the ECU/PCM for the memory is getting to the unit. There may be a intermittent connection to it causing this trouble. If that is good then the memory circuit may have a problem and you will have to swap the unit unless to can find a bad connection inside it. I have repaired bad ECUs in the past. They can fail but are usually the last place to find trouble.