diff --git a/core/src/rpc.rs b/core/src/rpc.rs
index dc05a64f52..70625a0cfb 100644
--- a/core/src/rpc.rs
+++ b/core/src/rpc.rs
@@ -1737,7 +1737,7 @@ fn _send_transaction(
     last_valid_slot: Slot,
 ) -> Result<String> {
     if transaction.signatures.is_empty() {
-        return Err(RpcCustomError::SendTransactionIsNotSigned.into());
+        return Err(RpcCustomError::TransactionSignatureVerificationFailure.into());
     }
     let signature = transaction.signatures[0];
     meta.send_transaction_service
@@ -2141,33 +2141,26 @@ impl RpcSol for RpcSolImpl {
 
         if !config.skip_preflight {
             if transaction.verify().is_err() {
-                return Err(RpcCustomError::SendTransactionPreflightFailure {
-                    message: "Transaction signature verification failed".into(),
-                }
-                .into());
+                return Err(RpcCustomError::TransactionSignatureVerificationFailure.into());
             }
 
             if meta.health.check() != RpcHealthStatus::Ok {
-                return Err(RpcCustomError::SendTransactionPreflightFailure {
-                    message: "RPC node is unhealthy, unable to simulate transaction".into(),
-                }
-                .into());
+                return Err(RpcCustomError::RpcNodeUnhealthy.into());
             }
 
             let preflight_commitment = config
                 .preflight_commitment
                 .map(|commitment| CommitmentConfig { commitment });
             let preflight_bank = &*meta.bank(preflight_commitment)?;
-            if let (Err(err), _log_output) =
+            if let (Err(err), logs) =
                 run_transaction_simulation(&preflight_bank, transaction.clone())
             {
-                // Note: it's possible that the transaction simulation failed but the actual
-                // transaction would succeed, such as when a transaction depends on an earlier
-                // transaction that has yet to reach max confirmations. In these cases the user
-                // should use the config.skip_preflight flag, and potentially in the future
-                // additional controls over what bank is used for preflight should be exposed.
                 return Err(RpcCustomError::SendTransactionPreflightFailure {
                     message: format!("Transaction simulation failed: {}", err),
+                    result: RpcSimulateTransactionResult {
+                        err: Some(err),
+                        logs: Some(logs),
+                    },
                 }
                 .into());
             }
@@ -4059,7 +4052,7 @@ pub mod tests {
         assert_eq!(
             res,
             Some(
-                r#"{"jsonrpc":"2.0","error":{"code":-32002,"message":"Transaction simulation failed: TransactionError::BlockhashNotFound"},"id":1}"#.to_string(),
+                r#"{"jsonrpc":"2.0","error":{"code":-32002,"message":"Transaction simulation failed: TransactionError::BlockhashNotFound","data":{"err":"BlockhashNotFound","logs":[]}},"id":1}"#.to_string(),
             )
         );
 
@@ -4075,7 +4068,7 @@ pub mod tests {
         assert_eq!(
             res,
             Some(
-                r#"{"jsonrpc":"2.0","error":{"code":-32002,"message":"Transaction simulation failed: TransactionError::SanitizeFailure"},"id":1}"#.to_string(),
+                r#"{"jsonrpc":"2.0","error":{"code":-32002,"message":"Transaction simulation failed: TransactionError::SanitizeFailure","data":{"err":"SanitizeFailure","logs":[]}},"id":1}"#.to_string(),
             )
         );
         let mut bad_transaction =
@@ -4091,7 +4084,7 @@ pub mod tests {
         assert_eq!(
             res,
             Some(
-                r#"{"jsonrpc":"2.0","error":{"code":-32002,"message":"RPC node is unhealthy, unable to simulate transaction"},"id":1}"#.to_string(),
+                r#"{"jsonrpc":"2.0","error":{"code":-32005,"message":"RPC node is unhealthy"},"id":1}"#.to_string(),
             )
         );
         health.stub_set_health_status(None);
@@ -4107,7 +4100,7 @@ pub mod tests {
         assert_eq!(
             res,
             Some(
-                r#"{"jsonrpc":"2.0","error":{"code":-32002,"message":"Transaction signature verification failed"},"id":1}"#.to_string(),
+                r#"{"jsonrpc":"2.0","error":{"code":-32003,"message":"Transaction signature verification failure"},"id":1}"#.to_string(),
             )
         );
 
@@ -4136,7 +4129,7 @@ pub mod tests {
         assert_eq!(
             res,
             Some(
-                r#"{"jsonrpc":"2.0","error":{"code":-32003,"message":"Transaction is not signed"},"id":1}"#.to_string(),
+                r#"{"jsonrpc":"2.0","error":{"code":-32003,"message":"Transaction signature verification failure"},"id":1}"#.to_string(),
             )
         );
     }
diff --git a/core/src/rpc_error.rs b/core/src/rpc_error.rs
index 6eea764fa4..d1796ee449 100644
--- a/core/src/rpc_error.rs
+++ b/core/src/rpc_error.rs
@@ -1,4 +1,5 @@
 use jsonrpc_core::{Error, ErrorCode};
+use solana_client::rpc_response::RpcSimulateTransactionResult;
 use solana_sdk::clock::Slot;
 
 const JSON_RPC_SERVER_ERROR_0: i64 = -32000;
@@ -6,6 +7,7 @@ const JSON_RPC_SERVER_ERROR_1: i64 = -32001;
 const JSON_RPC_SERVER_ERROR_2: i64 = -32002;
 const JSON_RPC_SERVER_ERROR_3: i64 = -32003;
 const JSON_RPC_SERVER_ERROR_4: i64 = -32004;
+const JSON_RPC_SERVER_ERROR_5: i64 = -32005;
 
 pub enum RpcCustomError {
     NonexistentClusterRoot {
@@ -18,11 +20,13 @@ pub enum RpcCustomError {
     },
     SendTransactionPreflightFailure {
         message: String,
+        result: RpcSimulateTransactionResult,
     },
-    SendTransactionIsNotSigned,
+    TransactionSignatureVerificationFailure,
     BlockNotAvailable {
         slot: Slot,
     },
+    RpcNodeUnhealthy,
 }
 
 impl From<RpcCustomError> for Error {
@@ -50,14 +54,14 @@ impl From<RpcCustomError> for Error {
                 ),
                 data: None,
             },
-            RpcCustomError::SendTransactionPreflightFailure { message } => Self {
+            RpcCustomError::SendTransactionPreflightFailure { message, result } => Self {
                 code: ErrorCode::ServerError(JSON_RPC_SERVER_ERROR_2),
                 message,
-                data: None,
+                data: Some(serde_json::json!(result)),
             },
-            RpcCustomError::SendTransactionIsNotSigned => Self {
+            RpcCustomError::TransactionSignatureVerificationFailure => Self {
                 code: ErrorCode::ServerError(JSON_RPC_SERVER_ERROR_3),
-                message: "Transaction is not signed".to_string(),
+                message: "Transaction signature verification failure".to_string(),
                 data: None,
             },
             RpcCustomError::BlockNotAvailable { slot } => Self {
@@ -65,6 +69,11 @@ impl From<RpcCustomError> for Error {
                 message: format!("Block not available for slot {}", slot,),
                 data: None,
             },
+            RpcCustomError::RpcNodeUnhealthy => Self {
+                code: ErrorCode::ServerError(JSON_RPC_SERVER_ERROR_5),
+                message: "RPC node is unhealthy".to_string(),
+                data: None,
+            },
         }
     }
 }