Can anybody tell me what can cause my a/c speedo tack and the overdrive to stop working all at the same time.Is it a sensor if so what one. Please help Thank you Jack snooky

 

Welcome to DF . Please do not post questions here in the FAQ section. Post them in the tech section if it is tech related. Thanks. I'll move this for you.

 

No one cause that I am aware of.

Any idiot lites on?

 

Check ALL the fuses too. Side of dash and pdc under hood.

 

There arnt any idiot lites on and the uses are good.All these thigs stoped working at the same time.

 

fuses are good.a man told me might be ign sw.could it be speed sensor or ground?

 

If I had to point at "one" item, it would be the PCM.

Tach is driven by the crank sensor, engine still runs, so, crank sensor is still good, and PCM is getting the signal.

Speedo is driven off the VSS in the back of the t-case... (if you are 4wd) tailshaft of trans if 2wd. It doesn't go thru the PCM, but, the PCM gets an input from it as well. If it isn't getting that signal, it won't ever shift into O/D, nor will TCC lock.

A/C is powered from a relay in the PDC, relay is controlled by the PCM. When you turn your heater to some flavor of A/C, and the fan is on, it powers the "request" circuit, which passes thru the high and low pressure switches. If the signal actually gets to the PCM, PCM trips the relay. I don't know if there are some circumstances where the PCM won't do just that, if some condition is/is not met.

Check the connectors at the PCM, see if one isn't loose, or dirty. Clean 'em all up, and see if that doesn't solve the issues.

 

If you decide to check and clean the pcm connections, remove the negative battery cable first.

 

This isn't a 94-98 diesel by chance is it? If so you have a crank sensor that is either out of adjustment (needs to be set to .020" air gap), or that has gone bad.

 

Hello I am not a mopar tech.I am a retired Nissan tech.One of you say it might be the pcm and one says it's the crank sensor.I know where the crank sensor is.But I am not shre what the pcm is or where it is located.Is it the power control modual?. Nissan had an ECM that was under the seat or under dash and even under the pas side floor on twin turbo z's. now where is it on a 97 2500 ram with 2 wheel drive auto Cummings turbo?