DodgeTalk Forum banner

Status
Not open for further replies.
1 - 20 of 39 Posts

·
Seating for 12
Joined
·
1,893 Posts
Discussion Starter #1
The DW calls me at work saying, the engine light came on and the van is very difficult to keep at 55mph. I told her to pull the van over. Next she calls back. The van will not go faster than 40mph. I told her again to pull over. Finally, she calls back. She pull the van over, I told her to do the on-off key trick. The code of P0121 was given.

P0121 (M) TPS Voltage Does Not Agree With MAP TPS signal does not correlate to MAP sensor signal.

P0121 (M) Accelerator Position Sensor (APPS) Signal Voltage Too Low APPS voltage input below the minimum acceptable voltage.

OK, so I know a little about this after searching the forums. It could be anything from a bad connection, damaged wires, bad TPS or MAP, A/C clutch relay or .... worst case needing a new PCM. :VHOT:

Without those sensors functioning properly, the PCM is going to default to a "limp-home" mode, which is running very rich and low mph down the road.

The van is sitting some 50 miles away from home right now. :WHT:

Anyone else had this code in the past?

Stev
 

·
4 Wheel Power Disc Brakes
Joined
·
5,828 Posts
I havent had this code, but 121 shows up in engine tech as MAP and TPS dissagree. I rebuilt a transmission not long ago and the ASTG manual said if the TPS sensor fails the computer will use the MAP sensor in limp-home mode. In so doing the engine may not run well and OD/lock-up will by controlied by MAP and will be more sensitive to shifting OD/lock-up.
It's also possibly the 5 volt supply from the ECU to the MAP, TPS, IAT and coolant temp has a broken wire at the MAP or TPS area.
If there was a short or no 5 volts from the ECU to these sensors there wouldn't be any voltage for the ECU to compare.
Quick test. Test for 5 volts at the sensors. This will tell if the wiring and ECU are OK.
--B-300--
 

·
Seating for 12
Joined
·
1,893 Posts
Discussion Starter #3
OK, I got the van home. Per a forum search, a person mentioned to diconnect the battery for 10 mins, and then try to drive it. Well, the PCM had to re-learn the ABS brakes right away since the roads were very snowy. They kept locking down too quickly until the fourth stop.

B-300, as for the 5V, a Dodge tech mentioned to test this when the van is in neutral and the engine is running in idle. Does this sound correct? Or will the 5V show up if the engine isn't running and the key is turned for the dash symbols to show up?

I did notice the OD/lockp-up too. In the begining drive home, it wouldn't lock into OD until 2 miles into the drive.

The gas pedal felt too soft when pressing it down unitl the 2/3rd point. Then the pedal required real effort to mash into the floor. Of course, the van had no get up and go either.

Right now, there is a blizzard outside and the sunlight is fading fast. I'll be busy on this Saturday morning indeed.

Now, where did I put that volt meter of mine. hmmmm

Stev
 

·
4 Wheel Power Disc Brakes
Joined
·
5,828 Posts
It will probably show 5 volts with the key on and definitely should show 5 volts with the engine running.
On the wiring diagram for a '93 terminal #4 is the 5 volt supply from the ECU (violet/white stripe). It goes to the TPS and to the MAP sensors.
I was wrong that the IAT and coolant temp sensors connect to this, at least on a '93.
--B-300--
 

·
Seating for 12
Joined
·
1,893 Posts
Discussion Starter #5
B-300,

I got a 2001, so those '93 and ECU's don't apply. ;)

The Haynes Repair Manual #30065 mentions to only run the engine when checking the MAP sensor since it needs to pull vaccum.

We're still caught up in the snow blizzard (day 3), so getting the van apart isn't the time. If the skys clear up by the afternoon, I'll get a portable electric heater in the van and work on the engine inside. Yes, I'll keep the heat further in the back so as the fuel isn't an issue.

If the volts test out OK, then I suspect the AC relay sensor. It's just a hunch right now as others have reported that the AC relay sensor could trhow a curve at the TPS & Map conflict.

Stev
 

·
4 Wheel Power Disc Brakes
Joined
·
5,828 Posts
Guess your right as many things changed in '96 up for OBD-II. Another thought occurs. Has the vacumn line to the MAP been broken or leaking?
Weather sounds horrible if fuel will freeze.
--B-300--
 

·
vanner
Joined
·
519 Posts
What is the DW?
 

·
Registered
Joined
·
246 Posts
On the gas pedal soft for the first 2/3 then hard to press for the last 1/3. Check the routing of the accel cable at the throttle body (especially at #2)
 

·
Registered
Joined
·
2,140 Posts
As mentioned, check the accelerator cable routing first. Could also be the TPS may be damaged internally causing the pedal problem? I'll see if I can find a TPS test procedure and post it.

SYMPTOM
P0121-TPS VOLTAGE DOES NOT AGREE WITH MAP

WHEN MONITORED
With the engine running and no MAP sensor or TPS DTC's set. Engine speed must be greater than 1600 RPM .

SET CONDITION
The PCM performs two separate tests. When the manifold vacuum is low, the TPS signal should be high. If the proper TPS voltage is not detected when the two conditions are met, a DTC will be set after 4 seconds .

POSSIBLE CAUSES
• High resistance in 5 volt supply circuit
• High resistance to ground in 5 volt supply circuit
• Intermittent condition
• High resistance in 5 volt supply circuit
• High resistance to ground in 5 volt supply circuit
• MAP sensor
• High resistance in MAP sensor signal circuit
• High resistance to ground in MAP sensor signal circuit
• High resistance in sensor ground circuit
• PCM
• Throttle position sensor
• High resistance in throttle position sensor signal circuit
• High resistance to ground in throttle position sensor signal circuit
• High resistance in sensor ground circuit
• PCM
 

·
Seating for 12
Joined
·
1,893 Posts
Discussion Starter #10 (Edited)
DANVAN said:
What is the DW?
LOL, that's a simple answer as many of the forums around the internet use this.

DW = Darling Wife or Dingbat Wife. It depends on how you read the statement and tone of the sentence structure. :D

DH = Darling Husband or Dingbat Husband. Dito. ;)
 

·
Seating for 12
Joined
·
1,893 Posts
Discussion Starter #11
Tech_John said:
On the gas pedal soft for the first 2/3 then hard to press for the last 1/3. Check the routing of the accel cable at the throttle body (especially at #2)
Everything there checked out A-OK. :cool:
 

·
Seating for 12
Joined
·
1,893 Posts
Discussion Starter #12
Chump said:
As mentioned, check the accelerator cable routing first. Could also be the TPS may be damaged internally causing the pedal problem? I'll see if I can find a TPS test procedure and post it.
Chump,

Good work. However, I managed to poke though my Haynes Repair Manual and followed all of the steps involved for testing out the TPS, MAP and IAC. All of these sensors were operating in their correct ranges. Bummer. Now what is the issue? A bad PCM ?!?

I did find that the TPS is like a potentiometer. As the gas pedal is pressed, the cable moves, the TB valves open and the TPS sensor rotates via the shaft axis. I took off the TPS, cleaned the contacts and carefully shook the sensor. I heard a little noise of something rattling around inside, but then it stopped. So, I place the TPS back onto the TB. I then restarted the van and the problem was still there. Bummer again.

Next, I visited the IAC. There was this gut feeling I had that this part could be the problem even though the TPS and MAP were reported being out of voltage range with each other. Per the advise of another Dodge forum on the internet, a DCX service tech, to me to give the TB the finger. After that all the problems went away. :huh: Well, this is a finger treatment you give to the IAC with the engine running at idle. Placing your index finger over the air-inlet port to the IAC on the TB, carefully and slowly choke off the air going into the port until the engine nearly stalls out. I did this several times since the IAC was pulsating. At the last time, I totally choked off the IAC until the engine stalled. This made the IAC to draw all the way back within it’s sensor housing. (NOTE: this is done only with the IAC mounted on the TB.)

The next step is critical. Take the negative battery terminal off for 2 mins. DO NOT touch the key until the 2 mins have passed.!!!! Now, turn the key off and reconnect the negative battery cable. This resets not only the PCM, but the other sensors for the TB.

Now, the final step was to turn the key back on for 5 seconds prior to a full start crank over. The IAC when it had stalled the engine from running drew all the way back in travel. Upon restarting, and waiting for the five seconds, I heard two distinct cracking noises from the IAC in movement as it went into it's position. Did this fix a sticky IAC or what was the finger trick suppose to do???

At first, I thought the advice was a little :crazy: ! BUT, with nothing to loose, I tried it. Not only did this wacky procedure work, but the engine behaves far better than when I had originally purchased it. It worked so well, that stomping on the pedal from a dead stop now lays a 15 foot streak of rubber on the street! The van NEVER did that before since I’ve owned it! I thought, what did this finger thing ?!?!?

The last thing I did was to replace the air filter. It wasn't totally bad, but I didn't get to it when I changed the oil last.

Now, my next step is to try the finger trick on the V6 B1500 since it's running like a dog with it's tail between the legs.
 

·
vanner
Joined
·
519 Posts
I always assumed it was the wife, just couldnt figure out what the letters stood for, never seen it before, thanks
 

·
Registered
Joined
·
270 Posts
I'm going to try this finger trick myself...I have no complaints with the power or the running of the van, but hey, it's free and can't hurt anything!
 

·
Seating for 12
Joined
·
1,893 Posts
Discussion Starter #15
So far, this finger trick has helped another friend of mine with a 5.2L engine in his truck. It may be a strange procedure, but it sure beats having the vehicle in limp-home mode for weeks on end like he had his.
 

·
Gone but not forgotten
Joined
·
1,288 Posts
Now, my next step is to try the finger trick on the V6 B1500 since it's running like a dog with it's tail between the legs.
Stev, did this trick work for the V-6 as well?
 

·
Seating for 12
Joined
·
1,893 Posts
Discussion Starter #17
Stev, did this trick work for the V-6 as well?
Yep, it works for the V6 3.9L as well. Although it didn't do much for it since this code never came up on that van.

The IAT mod would work best to get this engine peppy without spend big dollars towards a bigger exhaust and headers.

I've since sold the B1500 conversion. :bawl: It was my baby. However, with seven children, we couldn't possibly fit them all in it.
 

·
Gone but not forgotten
Joined
·
1,288 Posts
The IAT mod would work best to get this engine peppy without spend big dollars towards a bigger exhaust and headers.
From what I have read about IAT mods I won't be trying any. It seems more like "electronic 'snake oil'".
 

·
Seating for 12
Joined
·
1,893 Posts
Discussion Starter #19
All the IAT mod is doing is to move the sensor from the intake manifold to the air-housing. Thus, less heat is transferred to the sensor by the aluminum intake manifold. The PCM look up tables are then slide accordingly on it's table. The results are a little more Hp where the performance curve tends to fade off per gear climb.
 

·
Gone but not forgotten
Joined
·
1,288 Posts
All the IAT mod is doing is to move the sensor from the intake manifold to the air-housing. Thus, less heat is transferred to the sensor by the aluminum intake manifold. The PCM look up tables are then slide accordingly on it's table. The results are a little more Hp where the performance curve tends to fade off per gear climb.
Ok this one I would like to know more about it. All the ones I had found involved puting resistors inline with or by passing the IAT with them, which would not work.

Your description of the IAT mod will work and seems logical.

Where can I find more about this modification?
 
1 - 20 of 39 Posts
Status
Not open for further replies.
Top