no bus message
#1
08-23-2017, 09:43 AM
Join Date: Aug 2017
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no bus message
99 dodge ram 1500 with 5.2 just shut off going down the road. mileage flashed 4 times then no bus showing. Tried holding trip/reset while switching on truck everything worked. So cranked truck while running it just shut off.I redid the test again this time nothing happened then in the odometer it showed 920,921, and 999 any clue as to what this is
#2
08-23-2017, 07:20 PM
#3
09-03-2017, 04:48 PM
2000 Ram 1500 5.2L PCM Replacement
Greetings all! First time posting from a long-time reader, so if this isn't the right place please feel free to relocate the post.
I have a 2000 Ram 1500, 2WD, automatic trans, 5.2L, with about 134,000 miles. It's been a good vehicle with no major issues until recently. A couple of months ago it started randomly (so I thought) losing power, just completely shutting off, usually while in motion.
When it shuts down it does so with little or no warning - there's no bucking or chugging, the engine stops running, the gauges go to their "relaxed" positions (this includes the speedometer, which drops to zero even though I'm still moving), and I have a short window to coast to the side of the road or a convenient exit point. I'm avoiding bridges or steep inclines until I get this problem fixed. The odometer will flash four or five times and then display "no bus" and the check engine light will come on (so this isn't a complete loss of electrical power). The start will turn and engage, but the engine doesn't catch.
Now, I had thought this was a random problem, but a few weeks ago I noticed it only seemed to happen at relatively low speeds with the engine hot. It's never happened as a "won't start cold" problem. I've narrowed the problem down to it only happens when the temp gauge is within a couple of needle-widths of the center mark - which is unfortunately right around normal operating temp, and easily reached in stop & go traffic in NW Florida in the summer!
While "no bus" is displayed I can do the instrument cluster self test, and the cluster itself seems to test OK, but it shows error codes 920 (no vehicle speed from the PCM), 921 (no distance pulse from the PCM), and 999 (generic error condition). I think I've narrowed it down to crankshaft position, camshaft position, or PCM.
After one of these shutdowns, if I wait "a while" - five to thirty minutes - to let things things cool down, normal function resumes. If I've left the key in the run position I hear a "click" and the gauges come back to life, the odometer returns to a proper numeric display, and I can then start and resume operating. So, it's reasonable to think there's a sensor, or maybe the PCM, going bad, overheating, and shutting things down.
However, the next part has lead me to think the culprit is the PCM. When I do get this shutdown problem, as an alternative to waiting five to thirty minutes, to speed things along, I can get under the hood and press down slightly on connector C1 (the most inboard of the three) on the PCM. I hear a relay, pump, or motor engage in the engine compartment (I think this is the idle air control being pre-positioned), the gauges come back to life, and I can start again. If I'm understanding the wiring information correctly, connector C1 carries the signals from the crankshaft position sensor and the camshaft position sensor.
Now, I replaced the PCM with one ordered from one of the online vendors. It's not a difficult job, the PCM installs only one way, and it's very difficult to cross the connectors - but the truck will not start with that PCM. The vendor says this is a plug-and-drive operation, but not so for me. I've tried pulling the PCM fuses, disconnecting the battery negative, disconnecting both battery cables and connecting them and leaving the ignition in the run position, with no change. I can put my old PCM back in and I'm good to go, with the proviso that I still have the heat up & shutdown problem, but that tells me my removal & installation techniques are decent, and that either there is a problem with the new PCM, or there's some little trick to making the truck recognize the new PCM.
So, the questions:
Does it seem reasonable this is indeed a PCM issue? I think it is, but need a sanity check.
Are there any tricks that I haven't found that will get a replacement PCM working? I'm going to query the seller, but their web site says it's plug and play.
I have a 2000 Ram 1500, 2WD, automatic trans, 5.2L, with about 134,000 miles. It's been a good vehicle with no major issues until recently. A couple of months ago it started randomly (so I thought) losing power, just completely shutting off, usually while in motion.
When it shuts down it does so with little or no warning - there's no bucking or chugging, the engine stops running, the gauges go to their "relaxed" positions (this includes the speedometer, which drops to zero even though I'm still moving), and I have a short window to coast to the side of the road or a convenient exit point. I'm avoiding bridges or steep inclines until I get this problem fixed. The odometer will flash four or five times and then display "no bus" and the check engine light will come on (so this isn't a complete loss of electrical power). The start will turn and engage, but the engine doesn't catch.
Now, I had thought this was a random problem, but a few weeks ago I noticed it only seemed to happen at relatively low speeds with the engine hot. It's never happened as a "won't start cold" problem. I've narrowed the problem down to it only happens when the temp gauge is within a couple of needle-widths of the center mark - which is unfortunately right around normal operating temp, and easily reached in stop & go traffic in NW Florida in the summer!
While "no bus" is displayed I can do the instrument cluster self test, and the cluster itself seems to test OK, but it shows error codes 920 (no vehicle speed from the PCM), 921 (no distance pulse from the PCM), and 999 (generic error condition). I think I've narrowed it down to crankshaft position, camshaft position, or PCM.
After one of these shutdowns, if I wait "a while" - five to thirty minutes - to let things things cool down, normal function resumes. If I've left the key in the run position I hear a "click" and the gauges come back to life, the odometer returns to a proper numeric display, and I can then start and resume operating. So, it's reasonable to think there's a sensor, or maybe the PCM, going bad, overheating, and shutting things down.
However, the next part has lead me to think the culprit is the PCM. When I do get this shutdown problem, as an alternative to waiting five to thirty minutes, to speed things along, I can get under the hood and press down slightly on connector C1 (the most inboard of the three) on the PCM. I hear a relay, pump, or motor engage in the engine compartment (I think this is the idle air control being pre-positioned), the gauges come back to life, and I can start again. If I'm understanding the wiring information correctly, connector C1 carries the signals from the crankshaft position sensor and the camshaft position sensor.
Now, I replaced the PCM with one ordered from one of the online vendors. It's not a difficult job, the PCM installs only one way, and it's very difficult to cross the connectors - but the truck will not start with that PCM. The vendor says this is a plug-and-drive operation, but not so for me. I've tried pulling the PCM fuses, disconnecting the battery negative, disconnecting both battery cables and connecting them and leaving the ignition in the run position, with no change. I can put my old PCM back in and I'm good to go, with the proviso that I still have the heat up & shutdown problem, but that tells me my removal & installation techniques are decent, and that either there is a problem with the new PCM, or there's some little trick to making the truck recognize the new PCM.
So, the questions:
Does it seem reasonable this is indeed a PCM issue? I think it is, but need a sanity check.
Are there any tricks that I haven't found that will get a replacement PCM working? I'm going to query the seller, but their web site says it's plug and play.