99 vt calais auto, no speedo & stuck in 2nd gear

[JustynJules]

Thank you all for the help, it is appreciated. Thank you for the link 'dirty hands', that is very handy. Well it looks like I might have to risk driving the HJ for a while, it's on club rego so only limited kms per day but with 350hp at the back wheels, it will be quick trips into town :rockon:

 

[lout]

the speed sensor is an alternator type device, it outputs an ac signal
disconnect sensor from transmission and give it a spin and see if you get an ac signal
or with vehicle on stands or similar put vehicle in 2nd and measure output from speed sensor
with sensor removed from trans, again on stands or similar put in 2nd and see if you can see gears moving inside trans that would engage speed sensor
also use cluster diagnostics and see if pcm is getting any speed signal
measure signal at pcm C6 and D5
still behaving as pcm not seeing speed signal
stop replacing parts until you know what to replace

 

[Jxfwsf]

Cluster won't effect the trans, it gets told what speed to show from the pcm.
Lhm would have 2 gears (2nd/3rd) and would be triggered by a fault with a code, if none then it will operate normally.
It sounds like the trans is behaving like it isn't getting any power to it except this would throw every fault code related to the trans and cel would be on (just tested that theory, lots of fault codes).

VSS in these transmissions can't be removed and spun to check, they're a reluctor type with the ring pressed onto the output shaft of the trans, but even without a signal being supplied it would start in 1st (unless a code was thrown and we're back to the lhm theory)
and it'd eventually throw a code, pressure switch output to pcm would tell it it's in gear and rpm would tell it that is should be registering a speed.

How was the trans before this happened, any abnormal signs while driving, slipping, sloppy/delayed shifts?
A tech 2 or good scantool would be best then you could see what feedback was coming from the tran to the pcm (pressure switch info, what gear the selector is in etc etc) and what the pcm was telling the trans (what solenoids should be active blah blah)

The mechanic should be able to hook up a pressure gauge onto the trans and monitor fluid pressure, as there's no engagement of gears unless manually selecting 2nd.
What about reverse?


*edit* I keep coming back to mechanical fault in the trans (maybe faulty pcm for the speedo)... but pcm makes no sense for only engaging in 2nd and acting like neutral in other forward gears.
Maybe try it without the transmission fuse in (fuse box under the bonnet) and see what happens, (cel should light up) but see if it'll move forward when other gears.

 

[lout]

im still looking at no speedo signal to pcm
it fits all the symptoms except np CEL
possibly damaged wiring under car
i am guessing that the cel globe is faulty
is this a V6, scV6 or V8

DTC 24 - NO VEHICLE SPEED SENSOR (VSS) SIGNAL

CIRCUIT DESCRIPTION:The Vehicle Speed Sensor Assembly (VSS Assy.) provides vehicle speed information to the PCM. The VSS Assy. is a Permanent Magnet (PM) generator. The PM generator produces a pulsing AC voltage. The AC voltage level and the number of pulses increase with the speed of the vehicle. The PCM then converts the pulsing voltage to vehicle speed. The PCM uses this information for calculations. A scan tool can display the vehicle speed.When the PCM detects a low or no vehicle speed, when there is high engine speed in a drive range, then DTC 24 sets.DTC 24 SETS IF:· No TPS DTCs 21 or 22.· No TFP Val. Position Sw. DTC 28.· The transmission is not in Park or Neutral.· The TP angle is between 10-99%.· The engine speed is greater than 3000 RPM.· The vehicle speed is less than 3 km/h.· All of the above conditions met for 3 seconds.DTC 24 Will set if the VSS circuit is open from a standing stop. As the vehicle is accelerated the transmission will shift from 1st to 2nd gear at approximately 54 km/h. If the VSS signal is not present, DTC 24 will be set.TEST DESCRIPTION:The numbers below refer to the step numbers on the diagnostic chart.3. This step tests the integrity of the VSS Assy.4. This step tests the VSS Assy. circuit.DIAGNOSTIC AIDS:· Inspect the wiring for poor electrical connections at the PCM. Look for the following conditions:A bent terminalA backed out terminalA damaged terminalPoor terminal tensionA chafed wireA broken wire inside the insulationMoisture intrusionCorrosion· When diagnosing for an intermittent short or open condition, massage the wiring harness while watching the test equipment for a change.· Check circuits 831 and 832 for the proper connections to be sure they are clean and tight and the harness is routed correctly.· The scan tool should indicate a vehicle speed whenever the drive wheels are turning greater than 3 km/h.· The vehicle speed sensor resistance should be between 1470-2140 W at 20°C, and 2270-2820 W at 100° C.· Refer to "Intermittents" in Section 6C1-2B SYMPTOMS .When DTC 24 sets, the PCM will command second gear only, commands maximum line pressure, freeze shift adapts from being updated and inhibit TCC engagement.

 

[JustynJules]

A mine of information, thank you gentlemen :beer chug:
It was the ECU, replaced & now all working as normal.
In fact everything that was replaced wasn't a waste of money. The alternator was buggered, the tranny needed a service going by the condition of the filter & one of the solenoids and the battery was due to be renewed. The mechanic sent the dash cluster back, so in fact no money wasted and the mechanics here have learned quite a lot about the VT, they've asked me to print out your advices as future references for them.
Thank you all once again and have a safe & happy Easter