I’m in a real pickle here, so two months ago pulling into my driveway, the car just shut off, dash read “reduced engine power, service abs/traction, and check engine lights on. First thing I did was check the pcm for any acid leakage. Pcm is clean and no signs or corrosion, had the car towed to the nearest mechanic that had an available technician. Car threw p1518 code and one other (p06**) that I can’t remember and I’m unable to pull at the moment. Technician sent the unit to Flagship One, they had it tested and programmed and the unit is perfectly fine, got sent back and put it, TAC module was replaced, ignition switch replaced, grounds checked, voltages/resistance checked, battery is fairly brand new (from Costco), BCM is working fine, wiring to pcm/TAC is fine and car still won’t start, cranks just fine though. Picked up the car today and tech had explained that the PCM is perfectly fine however it’s not accepting the programming now and communication between the pcm and tac is (missing?). When it comes to electrical gremlins I’m at a total loss, tech is pulling his hair out trying to figure out what’s wrong here. I’m starting to lean towards a fuel system issue (no pressure) or a wiring/short issue (water seeps in through a crack near pcm). Any info is greatly appreciated! PS, fuel pump comes on just fine!

 

You need to measure the fuel pressure at the fuel rail should be close to 60psi, other things to check for is the presence of fuel injectors pulses, and pull a spark plug and check for spark. Is there tachometer movement when the car is cranking over if not there is a problem with the crank sensor or the wiring to it.

 

The battery is drained at the moment but last I remember there was movement on the tach, gauges were “twitching” when cranking. And would spark plugs throw pcm codes? I ask because the previous owner passed away and his son sold me the car and there are no records of when the last time the plugs were changed/inspected, I tried replacing them a while back but they won’t budge and feel seized.

 

While it could be a number of problems including grounds that need to be cleaned and dielectric greased, a wiring problem in the driver door near the rubber bellows, my bet would be the ignition switch. Typical bad ignition switch symptoms include sudden shut down, multiple DIC warnings including reduced power, low voltage, service abs/traction and check engine light.

Get the battery charged fully and try several SHORT cranks to see if it starts-- key OFF then try restart several times. Sometimes a failing ignition switch will make contact and allow a restart.

 

When you crank the engine , do you have any RPM indication in your cluster ?
If not , your crank sensor may not be working

 

UPDATE: I’m back home and I’m finally able to get into the car again, I will be double checking grounds and someone had mentioned I should try to spray some starter fluid straight into the throttle body to see if I can get the car to start, on my way to go buy a can from AZ I took the battery out to get it charged after coming home drained. To my surprise the battery tested as a bad battery. It’s a Costco battery and I never had high hopes for it, hoping the issue all along was the PCM wasn’t getting the right voltage thus throwing all those codes (It would make sense as to why everything else tested FINE!) Why the technician never bothered to check the battery before giving the car back is beyond me but I’ll be ordering an everstart battery from Walmart since I’ve heard good reviews about them or even a redtop. Hope the car starts with the new battery!

 

Crank shaft or Cam Sensor both fairly easy to replace

 

I got the new optima red top battery in, I proceeded to try starting the car, RPM gauge and Speedo were 100% unresponsive when cranking but all other gauges were fine (oil pressure, coolant, voltage) could my solution be a bad crank sensor?

 

Your tachometer should move a little when cranking, it is entirely possible that you have a bad crank sensor or the 5 volt supply to the sensor is missing.

 

Sounds like a bad crank sensor…you can check for spark and injector pulse to verify 100% but also can be the crank sensor wiring…let us know if you need help checking for injector pulse…you just need a 12 volt test light.

 

As you put a fresh red top battery in your car, recommend you base-line the troubleshooting;
Step 1)>Access the DIC now and write down all codes that are posted in the DIC memory now.
Step 2)>Clear all codes in the DIC memory,
Step 3)> Remove key from ignition, exit car and shut the door, go have your favorite beverage.
Step 4)> after you have finished your favorite beverage, go to your car, enter car, shut the door and attempt to start the car again.
Note> if....the car does start. observe check engine light, if the check engine light is blinking off-on-off shut car off immediately. If check engine light is not blinking and on solid let car warm up for a bit and then shut engine off.
Step 5)>Access the DIC now and write down all codes that are posted in the DIC memory now.

Post all DIC codes observed from Step 1 and all DIC codes observed from Step 5 to this thread.
When posting your DIC codes to this thread, it is important to know which step the codes were observed as we need to determine the difference between low voltage codes and hard fault codes.
Upon posting your codes we will have a better understanding of which direction to take in troubleshooting your car.

Cheers,
Goose

 

STEP 1:



10-PCM

NO COMM



28-TCS

C1255H

C1276 H C

U1255 H C



38- RTD

NO COMM



40-BCM

B0432 H

B0502 H

B0503 H

B0507 H

B0508 H

B2482 H C

B2578 H

B2583 H

B2592 H

B2593 H C

B2722 H

B2723 H

U1096 H

U1040 H



B0- RFA

U1255 H

U1096 H

U1064 H

U1000 H C



NO MORE CODES



STEP 5:

10-PCM

NO COMM



28-TCS

C1276 H C

U1255 H C



38-RTD

NO COMM



40-BCM

U1255 H



60-IPC

NO CODES



80-RADIO

NO CODES



99-HVAC

NO CODES



A0-LDCM

B2262 H

B2264 H



A1-RDCM

NO CODES



A6-SCM

NO CODES



B0-RFA

U1096 H

U1000 H C

NO MORE CODES



Note: PCM had codes

P0601 H C And

P1518 H C
Prior to sending it to flagship to get the PCM tested and the unit reprogrammed
And the car still did not start

 

For any module "NO COMM" you always check that modules powers and grounds...and grounds are not checked using resistance with an ohm meter....the PCM will have an ignition feed, battery feed and a ground.

 

I double checked the most important ground (which I believe is G201 if I’m not mistaken?) and it is nearly spotless and I don’t see any bent pins

 

NO NO NO...when are you guys gonna learn...LOL !!...a visual inspection is NOT good enough !!...that is not the PCM ground you are looking at BTW...the PCM ground is above the starter collocated with the battery negative cable above the starter...the PCM has 2 battery feeds and 1 ignition feed... you can use a 12 volt test light to check these powers and grounds but I check grounds using headlight bulbs depending on how much current the component draws...if it is a fuel pump that draws 5 amps I'll use a bulb that draws 5 amps...that 5 amps has to be able to return to the battery...remove the PCM connector C2 and with your test light connected to battery POSITIVE place the tip of the test light on those 4 ground terminals…to check power place test light on battery negative and see if the test light is bright at all 3 power sources...key off for the 2 battery feeds and key on for ignition feed…and check those 2 fuses...23 and 16...you can check with a DVOM and see if you see system voltage too.

 

Before doing any more mech work on your car can you please clarify the PCM repair history as the fault codes you posted for your PCM before being serviced was able to have COM but after being "serviced" has NO COM.....

From post #1 > Technician sent the unit to Flagship One, they had it tested and programmed and the unit is perfectly fine..
Remark> P0601 fault Code Definition for the 1997 Model Year Car
DTC P0601 Control Module Read Only Memory (ROM) Circuit Description
The PCM EEPROM contains data which is essential to running the engine and transmission. The PCM continuously checks the integrity of this data.
Conditions for Setting the DTC
The PCM is unable to correctly read data from the flash memory.
Action Taken When the DTC Sets
• The PCM illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
• The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Freeze Frame and/or Failure Records.
Diagnostic Aids
Replace the PCM even if this DTC exists only in history.

Comment> Need to reconfirm with Flagship One the repair history of your PCM and if they verified the EEPROM fault.

From post #1 Picked up the car today and tech had explained that the PCM is perfectly fine however it’s not accepting the programming now and communication between the pcm and tac is (missing?)
Question> When your Tech installed your PCM did they attempt any type of programming to the PCM while the PCM was installed in the car? Please advise?
Note> improper procedures used to program the PCM in-car will result in the PCM being "bricked" and require PCM replacement. Link to Tech Doc 1997 - 1999 Corvette: Service Bulletin: No Start Condition, Non-Functional PCM After Reprogramming (corvetteactioncenter.com)

DTC P1518 Throttle Actuator Control (TAC) Module Serial Data Circuit
Circuit Description The TAC Module and the PCM communicate via a dedicated serial data circuit. This serial data circuit is separate from any other serial data circuit on the vehicle. Accurate transmitting and receiving of serial data requires not only good circuit integrity but also adequate system voltage. This diagnostic monitors the accuracy of the serial data transmitted between the TAC Module and the PCM. If the PCM detects a loss of data or invalid data, this DTC sets.
Conditions for Setting the DTC
• The ignition switch is in the crank or run position.
• The ignition voltage is greater than 5.23 volts.
• Invalid or missing serial data messages are detected for a predetermined amount of time.
• All above conditions met for less than 1 second.

Action Taken When the DTC Sets
• The PCM will illuminate the Malfunction Indicator Light (MIL) when this diagnostic runs and fails.
• The Reduced Engine Power message displays on the drivers information center.
• The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Freeze Frame and/or Failure Records.
If no other TAC System DTCs are set, the TAC System will operate in Reduced Engine Power mode. If certain TAC System DTCs are set at the same time, the TAC System either defaults to a more tightly restricted mode of operation if the TAC determines that limited safe operation is possible, or the TAC commands the engine to shut down.
• If DTC P0606 is set with DTC P1518, the TAC commands an engine shut down.

DTC U1255 Generic Loss of Communications
Circuit Description
The Class 2 serial data line allows all the modules on the line to transmit information to each other as needed. Each module is assigned an ID and all the information sent out on the line is assigned a priority by which it is received. When the ignition switch is turned to the ON position each module begins to send and receive information. Each module on the Class 2 serial data line knows what information it needs to send out and what information it should be receiving. What the modules do not know is which module is supposed to send them the information. This information is only learned after the module has received the information it needs along with the ID of the module that sent the information. This information is then remembered until the ignition switch is turned off. If the EBTCM never recieves the information or the ID of the module that is supposed to send the information DTC U1255 will be set..

Conditions for Setting the DTC
The DTC can be set when the ignition is turned to the ON position, and the EBTCM does not recieve the PCM ID for 5 seconds.
Note PCM issue related DTC

DTC U1096 Loss of Communications with IPC
Circuit Description The serial data circuit is used to communicate information between systems. Each system connected to the serial data line is assigned its own recognition code (address). This code is used to identify which module or systems are communicating. Systems communicate with others by periodically sending a State of Health (SOH) message to each other. If the system sending the SOH message fails to receive a SOH message back, then a DTC identifying what system did not respond will set. Any system that also cannot communicate properly, will also store the appropriate communication DTC that was assigned to that system.

Conditions for Setting the DTC
• The BCM sends out a State of Health (SOH) message to the Instrument Panel Cluster (IPC), and no SOH message response was sent back.
• Condition must be present for 5 seconds.
Action Taken When the DTC Sets
• Stores a DTC U1096 in the BCM memory.
• No driver warning message will be displayed for this DTC
Conditions for Clearing the DTC
• This DTC requires an ignition cycle in order to change from current to history.
• The BCM receives a SOH message back from the IPC.
• A history DTC will clear after 50 consecutive ignition cycles if the condition for the malfunction is no longer present.
• Use the IPC clearing DTCs feature.
• Use a scan tool.
Diagnostic Aids
• If the problem is an intermittent loss of communications. Carefully inspect the serial data line and related components for the following intermittent conditions:
- There is an intermittent open or short (to ground or voltage) in the serial data line.
- Intermittent loss of communication with the IPC.
- Damaged or loose star connector terminals
• If the serial data line is shorted to ground or shorted to voltage, all systems connected to the same serial data line will not be able to communicate properly. Systems capable of storing loss of communication DTCs (DTCs with the letter U as a prefix) will have these codes stored in their memory. If a DTC U1096 is stored in the BCM memory, check for the same DTC stored in the Remote Function Actuation (RFA) system. The RFA system also monitors the SOH message from the IPC. If the RFA system has a DTC U1096 stored, check the IPC for an intermittent malfunction. If the RFA system does not have a DTC U1096 stored, check for an open in the serial data line between only the BCM and the IPC. The BCM must also be checked for intermittent operation due to a loss of power or ground to the BCM itself. After repairing a DTC U1096, clear all DTCs from all systems capable of storing this DTC.

DTC U1000 Class 2 Communication Malfunction
Circuit Description
The serial data circuit is used to communicate information between systems. Each system connected to the serial data line is assigned its own recognition code (address). This code is used to identify which module or systems are communicating. Systems communicate with others by periodically sending a State of Health (SOH) message to each other. When the ignition is first turned ON, the RFA system sends out a SOH message on the serial data line. When the RFA receives a response back, the RFA system is able recognize that system by "learning" its SOH message and recognition code. If the RFA system is unable "learn" this SOH message, the RFA system is unable to determine what system it lost communications with and a DTC will set.
Conditions for Setting the DTC
• The RFA system did not "learn" a SOH message and recognition code from any of the following systems:
- Body Control Module (BCM)
- Powertrain Control Module (PCM)
- Instrument Panel Cluster (IPC)
• This DTC can only set when the ignition is first turned ON.
• Condition must be present for 5 seconds.

DTC B2262 Horizontal Position Sensor Circuit (Left Door Mirror).
DTC B2264 Vertical Position Sensor Circuit (Left Door Mirror).

Cheers,
Goose

 

alright I have very good news, apologies for reviving this thread but the issue is still persisting. I have taken the car back from the old tech and sent it to a new place and WOW, I walked right into a crooked business with this place. My new tech managed to figure out the issue in less than 6 hours compared to the other place (3 months, and they found nothing). They showed me a diagram just like this and tested a few different colored wires, I’m not too savvy when it comes to anything electrical so please bear with me. First of all the first place I took the car too just completely lied to me and so did flagship one, my new tech informed me that all my wires were “tugged” as if someone manhandled them to pull them out and check them. Secondly nothing was replaced, TAC and ignition switch remain UNTOUCHED, and my PCM was dangling inside the car with my TAC module mounted on by one bolt. And third, my new tech attempted to get a reading from the PCM and lo-behold…it’s dead! It’s currently being sent off to Florida to get rebuilt and reprogrammed, they found no issues in wiring, everything is properly powered and working fine up until the PCM is plugged in.Moral of the story here, just because a certain business has the best reviews doesn’t always mean they’re actually the best!

 

97 and 98 had a funky PCM.
Hopefully it can be fixed.

Let us know how it comes out. And how much it costs.
People really gouge on those PCM’s if you have to find a used one. Saw one on EBay programmed for a corvette, like that’s something magic, for $1999!

Same pcm was used in 98 Camaros, just has a different program in it.

Ron